Chemistry Quiz: Predict Reactivity Using Periodic Table
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Predict Reactivity Using Periodic TableQuestion 1 of 20

Arrange these halogens in order of decreasing reactivity (most reactive to least reactive): fluorine (F, Group 17 Period 2), chlorine (Cl, Group 17 Period 3), bromine (Br, Group 17 Period 4).

Br > Cl > F
F > Cl > Br
Cl > F > Br
F > Br > Cl
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Chemistry Quiz

Chemistry Quiz: Predict Reactivity Using Periodic Table

Practice Predict Reactivity Using Periodic Table in Chemistry with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Predict Reactivity Using Periodic Table, giving you a quick way to practice the rules, question types, and explanations that matter most for Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

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Question 1

Arrange these halogens in order of decreasing reactivity (most reactive to least reactive): fluorine (F, Group 17 Period 2), chlorine (Cl, Group 17 Period 3), bromine (Br, Group 17 Period 4).

  1. Br > Cl > F
  2. F > Cl > Br (correct answer)
  3. Cl > F > Br
  4. F > Br > Cl
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Arranging by decreasing reactivity: fluorine (F, period 2) is smallest and most electronegative so most reactive, chlorine (Cl, period 3) is medium-sized and second most reactive, and bromine (Br, period 4) is largest of the three and least reactive—giving the order F > Cl > Br. Choice B (F > Cl > Br) correctly arranges the halogens by applying the group 17 trend where reactivity decreases as you go down the group due to decreasing electronegativity and increasing atomic size making electron gain less favorable. Choice A (Br > Cl > F) completely reverses the correct trend, incorrectly suggesting larger halogens are more reactive when the opposite is true—fluorine's small size and extreme electronegativity make it the most reactive element on the periodic table! For nonmetals (groups 16, 17, right side), reactivity decreases down the group because gaining electrons becomes harder as atoms get larger and electronegativity decreases. Remember the halogen reactivity order: F > Cl > Br > I > At, with fluorine so reactive it can even oxidize water and noble gases!

Question 2

A student compares how vigorously strontium (Sr, Group 2 Period 5) and magnesium (Mg, Group 2 Period 3) react with water. Which prediction is most accurate based on periodic position?

  1. Mg reacts more vigorously because it is lighter
  2. Sr reacts more vigorously because Group 2 reactivity increases down the group (correct answer)
  3. They react equally because both form +2+2 ions
  4. Neither reacts because only Group 1 metals react with water
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Strontium (period 5) reacts more vigorously than magnesium (period 3) because it's lower in group 2, with larger atoms and easier electron loss. Choice B correctly predicts strontium (Sr) is more vigorous by using the down-group increasing reactivity trend for group 2. The distractor in choice D fails by stating only group 1 reacts with water, when group 2 does too, just less intensely overall. Remember the metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Use the periodic table as a reactivity map—down groups 1-2 means more reactivity, and keep exploring to strengthen your understanding!

Question 3

A student compares the reactivity of fluorine (F, Group 17 Period 2), chlorine (Cl, Group 17 Period 3), and bromine (Br, Group 17 Period 4) in reactions where they gain an electron to form −1-1 ions. Which order correctly lists them from most reactive to least reactive?

  1. Br > Cl > F
  2. F > Cl > Br (correct answer)
  3. Cl > F > Br
  4. F > Br > Cl
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Fluorine (period 2) is most reactive, followed by chlorine (period 3), then bromine (period 4), due to decreasing electronegativity and ability to gain electrons down the group. Choice B correctly orders F > Cl > Br from most to least reactive by using the proper trend for halogens. The distractor in choice A fails by reversing the trend, likely mixing it up with metal reactivity that increases downward. Remember the metal vs nonmetal reactivity rule: for nonmetals (groups 16, 17, right side), reactivity decreases down the group because gaining electrons becomes harder as atoms get larger and electronegativity decreases. You're building strong skills—remember the extremes like fluorine's high reactivity for quick reference!

Question 4

Displacement reaction (halogens): Iodine (I2_2, Group 17 Period 5) is added to a solution of potassium chloride (KCl). Will iodine displace chlorine from chloride ions?

  1. Yes, because iodine is lower in the group and therefore more reactive
  2. Yes, because iodine has a larger atomic mass than chlorine
  3. No, because iodine is less reactive than chlorine (reactivity decreases down Group 17) (correct answer)
  4. No, because potassium compounds never participate in displacement reactions
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Iodine (period 5) cannot displace chlorine (period 3) from KCl because iodine is lower, less reactive, with lower electronegativity, making it worse at gaining electrons. Choice C correctly predicts no displacement by using the decreasing reactivity trend down group 17. The distractor in choice A fails by reversing the trend, claiming lower halogens are more reactive like metals. Displacement reaction predictions: a more reactive element can displace (replace) a less reactive element from a compound; for halogens: higher halogen displaces lower (chlorine displaces bromine or iodine, bromine displaces iodine). Keep practicing—these patterns will help you predict outcomes confidently!

Question 5

Displacement reaction (halogens): A container of potassium bromide solution (KBr) is available. A student bubbles chlorine gas (Cl2_2, Group 17 Period 3) into the solution. Will chlorine displace bromine (Br, Group 17 Period 4) from bromide ions in this reaction?

  1. Yes, because chlorine is more reactive than bromine (higher in Group 17) (correct answer)
  2. No, because bromine is more reactive than chlorine (lower in Group 17)
  3. No, because halogens cannot displace each other from compounds
  4. Yes, because bromine is heavier so it will be pushed out of the compound
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Chlorine (period 3) can displace bromine (period 4) from KBr because chlorine is higher in the group, more reactive, and better at gaining electrons to form ions. Choice A correctly predicts yes, displacement occurs, by applying the halogen trend where higher elements displace lower ones. The distractor in choice B fails by wrongly stating bromine is more reactive for being lower, confusing it with metal trends. Displacement reaction predictions: a more reactive element can displace (replace) a less reactive element from a compound; for halogens, higher halogen displaces lower (chlorine displaces bromine or iodine, bromine displaces iodine). Example: mixing chlorine with potassium bromide forms potassium chloride and releases bromine—use this to visualize trends!

Question 6

Three alkali metals—lithium (Li, Group 1 Period 2), sodium (Na, Group 1 Period 3), and potassium (K, Group 1 Period 4)—are each dropped into separate beakers of cold water. Which metal reacts most vigorously with the water?

  1. Li
  2. Na
  3. K (correct answer)
  4. All react equally vigorously because they are in the same group
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Potassium (period 4) is more reactive than sodium (period 3), which is more reactive than lithium (period 2), because potassium's outer electron is farthest from the nucleus and most easily lost. Choice C correctly predicts that potassium (K) reacts most vigorously by applying the increasing reactivity trend down group 1 for metals. The distractor in choice D fails by assuming equal reactivity just because they are in the same group, ignoring the down-group trend of decreasing ionization energy that makes lower elements more reactive. Remember the metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Use periodic table as a reactivity map: going down groups 1-2 = increasing metal reactivity, and keep practicing these trends to confidently predict reactions like this!

Question 7

Chlorine (Cl, Group 17 Period 3) is bubbled through a solution of potassium bromide (KBr), which contains bromide ions from bromine (Br, Group 17 Period 4). Based on halogen reactivity trends, what should happen?

  1. Chlorine displaces bromine because Cl is more reactive than Br (correct answer)
  2. Bromine displaces chlorine because Br is more reactive than Cl
  3. No reaction occurs because halogens cannot displace each other
  4. A reaction occurs only if the solution is heated because reactivity depends mainly on temperature, not position
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. In this displacement reaction, chlorine (period 3) is above bromine (period 4) in group 17, so chlorine is more reactive and can displace bromide ions from KBr, forming potassium chloride and releasing bromine. Choice A correctly predicts chlorine displaces bromine by applying the decreasing reactivity trend down group 17, where higher halogens displace lower ones. Choice B fails by reversing the trend—bromine is less reactive than chlorine, so it can't displace it; always remember halogen reactivity decreases downward! Displacement reaction predictions: a more reactive element can displace (replace) a less reactive element from a compound, like for halogens where higher ones displace lower (chlorine displaces bromine or iodine). Use periodic table as a reactivity map: going down group 17 = decreasing nonmetal reactivity, so position predicts displacement—great job applying this!

Question 8

Bromine (Br, Group 17 Period 4) is added to a solution containing iodide ions from potassium iodide (KI), where iodine is I (Group 17 Period 5). Based on halogen displacement trends, what is the correct prediction?

  1. Bromine displaces iodine because Br is more reactive than I (correct answer)
  2. Iodine displaces bromine because I is above Br in Group 17
  3. No reaction occurs because iodide is always more reactive than bromine
  4. A reaction occurs only if KI is replaced with KCl because chlorine is heavier
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. In this case, bromine (period 4) is above iodine (period 5), so bromine is more reactive and can displace iodide ions from KI, forming potassium bromide and releasing iodine. Choice A correctly predicts bromine displaces iodine by applying the decreasing reactivity trend down group 17, where higher halogens displace lower ones. Choice B fails by getting the positions wrong—iodine is below bromine, so less reactive and can't displace it; check periods carefully! Displacement reaction predictions: a more reactive halogen displaces a less reactive one, like bromine displacing iodine. Use periodic table as a reactivity map: going down group 17 = decreasing reactivity, so position predicts outcomes—superb!

Question 9

Two alkaline earth metals—strontium (Sr, Group 2 Period 5) and magnesium (Mg, Group 2 Period 3)—are each placed in cold water. Which is expected to show the more vigorous reaction based on periodic position?

  1. Mg, because lighter metals are always more reactive
  2. Sr, because reactivity increases down Group 2 (correct answer)
  3. Mg, because it is higher in Group 2 so it loses electrons more easily
  4. Neither reacts because Group 2 metals do not react with water
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Strontium (period 5) is more reactive than magnesium (period 3) because strontium's outer electrons are much farther from the nucleus, leading to easier loss and a more vigorous reaction with water. Choice B correctly predicts strontium (Sr) shows the more vigorous reaction by applying the increasing reactivity trend down group 2. Choice C fails by applying the halogen trend to metals—higher in group 2 means less reactive, not more; keep metal and nonmetal rules separate! For metals, reactivity increases down the group because ionization energy drops with size. This explains why strontium reacts more readily than magnesium—you're getting the hang of it!

Question 10

Three alkali metals—lithium (Li, Group 1 Period 2), sodium (Na, Group 1 Period 3), and potassium (K, Group 1 Period 4)—are each placed in separate beakers of cold water. Which metal is expected to react most vigorously with the water based on periodic position?

  1. Li
  2. Na
  3. K (correct answer)
  4. All react equally because they are in Group 1
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Potassium (period 4) is more reactive than sodium (period 3), which is more reactive than lithium (period 2), because potassium's outer electron is farthest from the nucleus and most easily lost. Choice C correctly predicts that potassium (K) will react most vigorously by applying the increasing reactivity trend down group 1 for metals. Choice D fails because, although all are in group 1, reactivity does not stay equal—it increases down the group due to decreasing ionization energy, so they don't react equally. Remember the metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Use periodic table as a reactivity map: going down groups 1-2 = increasing metal reactivity, and position predicts how vigorously they'll react with water—keep practicing these trends, you're doing great!

Question 11

Arrange these halogens in order of decreasing reactivity (most reactive to least reactive), given their periodic positions: chlorine (Cl, Group 17 Period 3), bromine (Br, Group 17 Period 4), iodine (I, Group 17 Period 5).

  1. I > Br > Cl
  2. Cl > Br > I (correct answer)
  3. Br > Cl > I
  4. Cl > I > Br
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Given their positions, chlorine (period 3) is more reactive than bromine (period 4), which is more reactive than iodine (period 5), so the decreasing order is Cl > Br > I. Choice B correctly arranges them by applying the decreasing reactivity trend down group 17 for nonmetals. Choice A fails by reversing the order—iodine is least reactive, not most; remember, for halogens, top is most reactive! For nonmetals (groups 16, 17, right side), reactivity decreases down the group because gaining electrons becomes harder as atoms get larger and electronegativity decreases. Remember the extremes: chlorine is quite reactive, but iodine is mild—excellent progress!

Question 12

Two alkaline earth metals—magnesium (Mg, Group 2 Period 3) and calcium (Ca, Group 2 Period 4)—are placed in separate containers of water. Which is expected to react faster with water based on periodic trends in Group 2?

  1. Mg, because it is higher in the group so it is more reactive
  2. Ca, because reactivity increases down Group 2 (correct answer)
  3. They react at the same rate because both form 2+2+ ions
  4. Neither reacts with water because Group 2 metals are unreactive
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Calcium (period 4) is more reactive than magnesium (period 3) because calcium's outer electrons are farther from the nucleus and easier to lose, leading to a faster reaction with water. Choice B correctly predicts calcium (Ca) reacts faster by applying the increasing reactivity trend down group 2 for metals. Choice A fails by applying the wrong trend—being higher in the group means less reactive for metals, not more; don't mix it up with halogens! Remember the metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. This is why calcium fizzes more vigorously than magnesium in water—keep up the good work!

Question 13

Halogen reactivity decreases down Group 17. A more reactive halogen can displace a less reactive halogen from its salt. If bromine (Br, Period 4) is added to a potassium iodide (KI) solution, what is the correct prediction?

  1. No—bromine cannot displace iodine because iodine is more reactive than bromine
  2. Yes—bromine will displace iodine because bromine is more reactive than iodine (correct answer)
  3. Yes—bromine will displace iodine because iodine is more reactive than bromine
  4. No—displacement reactions only occur for metals, not halogens
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Bromine (period 4) is more reactive than iodine (period 5) due to its smaller size and higher electronegativity, so it can displace iodine from KI by gaining electrons more readily. Choice B correctly predicts reactivity by applying the appropriate periodic trend for the element group (increasing down for metals, decreasing down for halogens). Choice A fails by applying the wrong group trend, claiming iodine is more reactive when actually bromine is, due to decreasing reactivity down the group. Displacement reaction predictions: a more reactive element can displace (replace) a less reactive element from a compound—for halogens, higher ones displace lower (bromine displaces iodine). Use the periodic table as a reactivity map: going down group 17 means decreasing nonmetal reactivity, so position predicts displacement like in this bromine-iodine example!

Question 14

Halogens (Group 17) react with metals to form ionic compounds, and halogen reactivity decreases down the group. Consider fluorine (F, Period 2), chlorine (Cl, Period 3), bromine (Br, Period 4), and iodine (I, Period 5). Which halogen is the most reactive?

  1. Iodine (I)
  2. Bromine (Br)
  3. Chlorine (Cl)
  4. Fluorine (F) (correct answer)
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Fluorine (period 2) is the most reactive because its small size gives it the highest electronegativity, making it easiest for it to gain an electron compared to the larger halogens lower in the group. Choice D correctly predicts reactivity by applying the appropriate periodic trend for the element group (increasing down for metals, decreasing down for halogens). Choice A fails by applying the wrong group trend, treating halogens like metals where reactivity increases down, but actually iodine is least reactive due to its larger size and lower electronegativity. For nonmetals (groups 16, 17, right side), reactivity decreases down the group because gaining electrons becomes harder as atoms get larger and electronegativity decreases—this opposite-trend pattern makes sense: metals lose electrons (easier when large), nonmetals gain electrons (easier when small). Remember the extremes for quick reference, like fluorine reacting with almost everything while iodine is mild, and use position to predict: going down group 17 means decreasing nonmetal reactivity!

Question 15

Alkali metal reactivity increases down Group 1. A teacher compares sodium (Na, Period 3) and rubidium (Rb, Period 5) in separate water demonstrations. Which prediction is most accurate?

  1. Sodium reacts more vigorously because it has a smaller atomic mass
  2. Rubidium reacts more vigorously because it is lower in Group 1 (correct answer)
  3. They react equally vigorously because both form +1 ions
  4. Neither reacts with water because alkali metals only react with acids
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Rubidium (period 5) reacts more vigorously than sodium (period 3) because its lower position means even lower ionization energy, making its reaction with water more explosive. Choice B correctly predicts reactivity by applying the appropriate periodic trend for the element group (increasing down for metals, decreasing down for halogens). Choice A fails by using a wrong reactivity factor, like atomic mass, when the key is position and ionization energy trend, not mass. The metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Remember the extremes for quick reference, like rubidium's intense reaction compared to sodium's, and use the periodic table as a reactivity map: lower in group 1 means more vigorous!

Question 16

Alkaline earth metal reactivity increases down Group 2. You have beryllium (Be, Period 2), magnesium (Mg, Period 3), and calcium (Ca, Period 4). Which is expected to be the most reactive with water (qualitatively, most vigorous) among these three?

  1. Beryllium (Be)
  2. Magnesium (Mg)
  3. Calcium (Ca) (correct answer)
  4. Magnesium (Mg) and calcium (Ca) are equally reactive because they are next to each other
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Calcium (period 4) is the most reactive among these because its lower position means lowest ionization energy, leading to the most vigorous reaction with water compared to magnesium (period 3) and beryllium (period 2). Choice C correctly predicts reactivity by applying the appropriate periodic trend for the element group (increasing down for metals, decreasing down for halogens). Choice A fails by reversing the trend, picking beryllium as most reactive when it's the least due to its small size and high ionization energy. The metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Remember the extremes for quick reference, like calcium's reactivity versus beryllium's reluctance to react with water, and use position to predict!

Question 17

Three alkali metals (Group 1)—lithium (Li, Period 2), sodium (Na, Period 3), and potassium (K, Period 4)—are each dropped into separate beakers of cold water. Which metal is expected to react most vigorously with water based on periodic position?

  1. Lithium (Li)
  2. Sodium (Na)
  3. Potassium (K) (correct answer)
  4. All three react equally vigorously
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Since potassium (K) is in Period 4, sodium (Na) is in Period 3, and lithium (Li) is in Period 2, potassium has the largest atomic radius with its valence electron farthest from the nucleus, making it the most reactive with water—it will fizz violently, may catch fire, and zoom around the water surface! Choice C correctly identifies potassium as most reactive because it's lowest in Group 1 among the three options, following the trend of increasing reactivity down the group. Choice D incorrectly suggests equal reactivity, ignoring the significant periodic trend that makes potassium much more reactive than lithium. The metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. Remember that alkali metal reactions with water get progressively more violent as you go down the group—lithium fizzes gently, sodium may ignite, potassium definitely ignites, and cesium explodes!

Question 18

A displacement test is attempted by adding iodine (I2_2, Group 17, Period 5) to a solution of potassium chloride (KCl). Based on periodic trends for Group 17, will iodine displace chlorine from chloride ions?

  1. Yes, iodine will displace chlorine because it is lower in the group
  2. Yes, iodine will displace chlorine because it has a larger atomic mass
  3. No, iodine will not displace chlorine because iodine is less reactive than chlorine (correct answer)
  4. No, because potassium ions prevent all displacement reactions
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Since iodine (I, Period 5) is lower in Group 17 than chlorine (Cl, Period 3), iodine is less reactive and cannot displace chlorine from chloride ions—no reaction will occur because iodine atoms cannot pull electrons away from the more tightly held chloride ions! Choice C correctly predicts no displacement because iodine is less reactive than chlorine, following the rule that only more reactive halogens can displace less reactive ones. Choice A incorrectly suggests iodine will displace chlorine based on being lower in the group, but this reverses the halogen reactivity trend—being lower makes halogens LESS reactive, not more! Displacement reaction predictions: a more reactive element can displace (replace) a less reactive element from a compound. Remember: for halogens, reactivity decreases down the group, so displacement only works upward—chlorine displaces bromine and iodine, bromine displaces only iodine, but iodine cannot displace any halogen above it!

Question 19

Three halogens (Group 17)—chlorine (Cl, Period 3), bromine (Br, Period 4), and iodine (I, Period 5)—are compared for how readily they react by gaining an electron. Which halogen is expected to be most reactive?

  1. Iodine (I)
  2. Bromine (Br)
  3. Chlorine (Cl) (correct answer)
  4. All three are equally reactive because they are in Group 17
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For halogens (group 17), reactivity decreases down the group—the opposite of metals! Fluorine is the most reactive halogen, then chlorine, then bromine, then iodine because smaller halogen atoms attract electrons more strongly (higher electronegativity) and can gain the electron needed to complete their octet more readily. Among the three halogens given, chlorine (Cl, Period 3) is smallest, followed by bromine (Br, Period 4), then iodine (I, Period 5), which means chlorine has the highest electronegativity and strongest pull on electrons, making it the most reactive—chlorine readily displaces both bromine and iodine from their compounds! Choice C correctly identifies chlorine as most reactive because it's highest in Group 17 among the three options, following the trend of decreasing reactivity down the group for nonmetals. Choice D incorrectly claims equal reactivity, missing the significant trend that makes chlorine much more reactive than iodine. For nonmetals (groups 16, 17, right side), reactivity decreases down the group because gaining electrons becomes harder as atoms get larger and electronegativity decreases. Remember the halogen reactivity series: F > Cl > Br > I—this explains why chlorine is used to disinfect water (very reactive) while iodine is mild enough to use as an antiseptic on skin!

Question 20

Four Group 2 metals are compared for how readily they react with water: beryllium (Be, Period 2), magnesium (Mg, Period 3), calcium (Ca, Period 4), and strontium (Sr, Period 5). Which is expected to be least reactive with water based on periodic position?

  1. Strontium (Sr)
  2. Calcium (Ca)
  3. Magnesium (Mg)
  4. Beryllium (Be) (correct answer)
Explanation: This question tests your ability to predict relative reactivity of elements using their positions on the periodic table, particularly for highly reactive groups like alkali metals (group 1), alkaline earth metals (group 2), and halogens (group 17). For alkali metals (group 1) and alkaline earth metals (group 2), reactivity increases as you go down the group because atoms get larger with more electron shells, making the outermost electrons farther from the nucleus and easier to remove—this means lower ionization energy and faster reaction when losing electrons to form positive ions. Among the four Group 2 metals, beryllium (Be, Period 2) is highest on the periodic table with the smallest atomic radius and fewest electron shells, making its valence electrons closest to the nucleus and most tightly held—beryllium doesn't react with water at all, even when heated! Choice D correctly identifies beryllium as least reactive because it's in the highest period (Period 2) among all Group 2 options, following the trend where reactivity increases down the group. Choice A incorrectly suggests strontium is least reactive, when strontium (Period 5) is actually highly reactive with water due to its large size and low ionization energy. The metal vs nonmetal reactivity rule: for metals (groups 1, 2, left side of periodic table), reactivity increases down the group because losing electrons becomes easier as atoms get larger and ionization energy decreases. The Group 2 reactivity series shows dramatic differences: beryllium doesn't react with water, magnesium needs steam, calcium reacts with cold water, and strontium reacts vigorously—all predictable from their periodic positions!