Aluminum (Al) is a Group 13 element with atomic number 13. It commonly forms Al . Which explanation best supports this ion charge?
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Aluminum (Al) is a Group 13 element with atomic number 13. It commonly forms Al . Which explanation best supports this ion charge?
Aluminum (Al) is a Group 13 element with atomic number 13. It commonly forms Al . Which explanation best supports this ion charge?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Aluminum has atomic number 13, so a neutral atom has 13 electrons; to form Al³⁺, it loses 3 electrons, resulting in 10 electrons and a configuration matching neon (1s² 2s² 2p⁶). Choice B correctly explains ion formation by identifying that electrons are lost and connecting this to achieving stable noble gas configuration. Choice A fails because it suggests aluminum gains electrons, forming a negative ion, but group 13 metals lose three electrons to form +3 ions. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting! Impressive work—ions are your strength now!
Nitrogen (N) has atomic number 7 and is in Group 15. It commonly forms the nitride ion, N³⁻. Which statement best explains why N forms a 3− ion?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For nitrogen (N, atomic number 7, electron configuration 1s² 2s² 2p³), it gains 3 electrons to fill its 2p orbital, resulting in N³⁻ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable octet—terrific progress in mastering ion stability! Choice A correctly explains ion formation by identifying that nitrogen gains 3 electrons to achieve the stable neon configuration, forming N³⁻. Choice B fails because nitrogen, as a nonmetal, gains electrons rather than losing them, and losing would form a positive ion, not N³⁻; choices C and D suggest gaining or losing 5, which wouldn't achieve an octet or match neon. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!
Bromine (Br) is a Group 17 element with atomic number 35. It forms the ion Br . Which statement best explains the formation of Br from Br?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Bromine has atomic number 35, so a neutral atom has 35 electrons; to form Br⁻, it gains 1 electron, resulting in 36 electrons and a configuration matching krypton. Choice A correctly explains ion formation by identifying that electrons are gained and connecting this to achieving stable noble gas configuration. Choice B fails because it suggests bromine loses an electron, forming a positive ion, but group 17 nonmetals gain one electron to form -1 ions. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting! Superb understanding—you're almost there!
Oxygen (O) has atomic number 8 and is in Group 16. It commonly forms the oxide ion, O²⁻. Which choice correctly describes what must happen for O²⁻ to form and why?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For oxygen (O, atomic number 8, electron configuration 1s² 2s² 2p⁴), it gains 2 electrons to fill its 2p orbital, resulting in O²⁻ with 10 electrons and the configuration 1s² 2s² 2p⁶, matching neon's stable octet—you're doing wonderfully understanding this process! Choice A correctly explains ion formation by identifying that oxygen gains 2 electrons to achieve the stable neon configuration, forming O²⁻. Choice B fails because oxygen, as a nonmetal, gains electrons rather than losing them, and losing would form a positive ion, not O²⁻; choices C and D suggest gaining 1 or losing 6, which wouldn't complete the octet or match neon. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably! Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!
Chlorine (Cl) is a group 17 element with atomic number 17 and an electron configuration ending in 3s23p5. It commonly forms the chloride ion Cl⁻. Which choice correctly explains the change from Cl to Cl⁻?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Chlorine has 17 electrons with configuration ending in 3s²3p⁵—that's 7 valence electrons, just one shy of a complete octet! When Cl gains 1 electron, it fills that last spot in the 3p sublevel (3p⁶), giving it 18 electrons total, exactly matching argon's stable noble gas configuration. This creates Cl⁻ with 17 protons but 18 electrons, producing the -1 charge. Choice A correctly identifies that Cl gains 1 electron to complete its valence shell (3p⁶), achieving argon's stable configuration and forming Cl⁻—this is exactly right! Choice B incorrectly suggests Cl loses an electron to form Cl⁺, but nonmetals like chlorine gain electrons, not lose them—losing would leave Cl with only 6 valence electrons, farther from stability. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!
Sulfur (S) is a group 16 element with atomic number 16. It commonly forms S²⁻. Which choice correctly connects sulfur’s group position to the ion charge and electron change?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Sulfur, being in group 16, has 6 valence electrons and needs 2 more to complete its octet. When S gains 2 electrons, it goes from 16 to 18 electrons total, achieving the same electron configuration as argon (Ar): a complete outer shell with 8 valence electrons. This creates S²⁻ with 16 protons but 18 electrons, producing the -2 charge. Choice A correctly connects sulfur's group 16 position to its tendency to gain 2 electrons (since 8 - 6 = 2), forming S²⁻ with argon's electron configuration—this perfectly explains the pattern! Choice B incorrectly suggests S loses 6 electrons to form S⁶⁺, but nonmetals gain electrons, and losing 6 would leave sulfur with only 10 electrons (like neon) but would require enormous energy. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!
Magnesium (Mg) is a group 2 element with atomic number 12 and an electron configuration ending in 3s2. It commonly forms Mg²⁺. How does a neutral Mg atom become Mg²⁺, and why is the +2 charge typical?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Magnesium has 12 electrons with its outermost electrons in the 3s² sublevel—these are its only 2 valence electrons. When Mg loses both of these 3s electrons, it's left with 10 electrons, giving it the exact same electron configuration as neon (Ne): 1s²2s²2p⁶. This creates Mg²⁺ with 12 protons but only 10 electrons, resulting in the +2 charge. Choice C correctly explains that Mg loses its 2 valence electrons to achieve neon's stable noble-gas configuration, forming Mg²⁺—this perfectly describes the process! Choice A incorrectly suggests Mg gains electrons to form Mg²⁻, but metals always lose electrons, never gain them—gaining would move Mg away from noble gas stability. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!
Fluorine (F) is a group 17 element with atomic number 9 and electron configuration ending in 2p5. It forms F⁻. How many electrons are gained or lost when forming F⁻, and what stability reason best explains it?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Fluorine has 9 electrons with configuration ending in 2p⁵—that's 7 valence electrons, just one electron away from a complete octet! When F gains 1 electron, it fills that last spot in the 2p sublevel (2p⁶), giving it 10 electrons total with the exact same configuration as neon (Ne): 1s²2s²2p⁶. This creates F⁻ with 9 protons but 10 electrons, producing the -1 charge. Choice B correctly explains that F gains 1 electron to complete its valence shell (2p⁶), becoming like neon and forming F⁻—this is exactly right! Choice A incorrectly suggests F loses an electron, but fluorine is a nonmetal that gains electrons—losing would leave F with only 6 valence electrons, moving it farther from the stable octet. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!
Aluminum (Al) is in group 13 and has atomic number 13. It commonly forms Al³⁺. Which statement best explains why Al forms a 3+ ion?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Aluminum has 13 electrons with 3 valence electrons in its outer shell (3s²3p¹). When Al loses all 3 of these valence electrons, it's left with 10 electrons, giving it the same electron configuration as neon (Ne): 1s²2s²2p⁶—a complete, stable outer shell! This creates Al³⁺ with 13 protons but only 10 electrons, resulting in the +3 charge. Choice B correctly explains that Al loses its 3 valence electrons to reach neon's stable noble-gas configuration, forming Al³⁺—this perfectly describes why aluminum forms a 3+ ion! Choice A incorrectly suggests Al gains electrons to form Al³⁻, but aluminum is a metal that loses electrons—gaining would give Al 16 electrons, which doesn't match any noble gas configuration. The ion charge prediction recipe from periodic table: (1) Identify group number: Groups 1, 2, 13 are metals that LOSE electrons. Groups 15, 16, 17 are nonmetals that GAIN electrons. (2) Predict charge from group: Group 1 loses 1 → forms +1. Group 2 loses 2 → forms +2. Group 13 loses 3 → forms +3. Group 15 gains 3 → forms -3. Group 16 gains 2 → forms -2. Group 17 gains 1 → forms -1. The pattern: for metals, positive charge equals group number (mostly). For nonmetals, negative charge equals 8 minus group number (to reach 8 valence). (3) Verify with noble gas: Which noble gas is nearest? Metals lose to match previous noble gas (sodium matches neon by losing 1). Nonmetals gain to match next noble gas (chlorine matches argon by gaining 1). This method predicts common ions reliably!
Oxygen (O) has atomic number 8 and 6 valence electrons (group 16). It commonly forms the oxide ion O²⁻. Which option best explains why oxygen forms a 2− ion?
Explanation: This question tests your understanding of why and how atoms form ions by losing or gaining electrons to achieve stable electron configurations like those of noble gases. Atoms form ions to achieve stable electron configurations, typically matching the nearest noble gas (helium, neon, argon) which have full outer electron shells: metals (left side of periodic table, groups 1-3) form positive ions (cations) by LOSING their few valence electrons, leaving them with a full inner shell matching the previous noble gas. Nonmetals (right side, groups 15-17) form negative ions (anions) by GAINING electrons to complete their outer shells and match the next noble gas. For example, sodium (11 electrons, configuration ending in 3s¹) loses that 1 outer electron to form Na⁺ with 10 electrons, matching neon's stable configuration. Chlorine (17 electrons, ending in 3p⁵, needs 1 more for full octet) gains 1 electron to form Cl⁻ with 18 electrons, matching argon's configuration. The drive toward noble gas stability—full outer shells—explains why specific charges form! Oxygen has 8 electrons total with 6 in its valence shell (2s²2p⁴), meaning it needs 2 more electrons to complete its octet. When O gains 2 electrons, both fill empty spots in the 2p sublevel, giving oxygen 10 electrons total with configuration 1s²2s²2p⁶—exactly matching neon's stable noble gas configuration! This creates O²⁻ with 8 protons but 10 electrons, producing the -2 charge. Choice B correctly explains that O gains 2 electrons to complete an octet in its valence shell, achieving neon's stable configuration and forming O²⁻—this is precisely what happens! Choice A incorrectly suggests O loses electrons to form O²⁺, but oxygen is a nonmetal that gains electrons—losing would leave O with only 4 valence electrons, moving it farther from the stable octet. Electron bookkeeping for ions: if atom has 11 electrons and forms +1 ion, it LOST 1 electron, leaving 10. If atom has 17 electrons and forms -1 ion, it GAINED 1 electron, giving 18. The math: ion electrons = atomic number - charge. For Na⁺: 11 - (+1) = 10 electrons. For Cl⁻: 17 - (-1) = 18 electrons (subtracting negative adds!). For Mg²⁺: 12 - (+2) = 10 electrons. Quick check: cations should have fewer electrons than protons (positive charge makes sense), anions should have more electrons than protons (negative charge makes sense). If your ion doesn't match this, recheck your electron counting!