Oxidation Number - MCAT Chemical and Physical Foundations of Biological Systems
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What is the oxidation state of sulfur in H2SO4?
What is the oxidation state of sulfur in H2SO4?
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Since there is no overall charge on the compound the oxidation states must cancel out. Although the oxidation state of hydrides are +1, there are two in the compound that must be accounted for. The same is true for oxygen; although the oxidation number of oxygen is -2, there are four oxygens present accounting for a total of -8. The +2 state contribution from the hydrides and -8 from the oxygens results in a -6 charge. The oxidation state on sulfur must be +6 for the molecule to be neutral.
Since there is no overall charge on the compound the oxidation states must cancel out. Although the oxidation state of hydrides are +1, there are two in the compound that must be accounted for. The same is true for oxygen; although the oxidation number of oxygen is -2, there are four oxygens present accounting for a total of -8. The +2 state contribution from the hydrides and -8 from the oxygens results in a -6 charge. The oxidation state on sulfur must be +6 for the molecule to be neutral.
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What is the oxidation number of chromium in calcium dichromate (CaCr2O7)?
What is the oxidation number of chromium in calcium dichromate (CaCr2O7)?
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Since the calcium ion has a charge of +2, the dichromate anion must have a charge of -2. Oxygen always has an oxidation number of -2, so the seven oxygens in the molecule have a total number of -14. That leaves a charge of +12 that the two chromiums must balance out (-2 - (-14) = 12). Each chromium must therefore have an oxidation number of +6.
Since the calcium ion has a charge of +2, the dichromate anion must have a charge of -2. Oxygen always has an oxidation number of -2, so the seven oxygens in the molecule have a total number of -14. That leaves a charge of +12 that the two chromiums must balance out (-2 - (-14) = 12). Each chromium must therefore have an oxidation number of +6.
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What is the oxidation state of nitrogen in HNO3?
What is the oxidation state of nitrogen in HNO3?
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When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
When applying the oxidation state to HNO3, hydrogen has a +1 oxidation state, and each of the oxygen molecules has a –2 oxidation state. Since there is only one hydrogen molecule and three oxygen molecules, the oxidation state of nitrogen must balance out the charge of the hydrogen molecule and oxygen molecules combined.
Nitrogen must have a +5 oxidation state.
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
When applying the oxidation state to HNO3, hydrogen has a +1 oxidation state, and each of the oxygen molecules has a –2 oxidation state. Since there is only one hydrogen molecule and three oxygen molecules, the oxidation state of nitrogen must balance out the charge of the hydrogen molecule and oxygen molecules combined.
Nitrogen must have a +5 oxidation state.
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What is the oxidation number of hydrogen in NaH?
What is the oxidation number of hydrogen in NaH?
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When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
Following the oxidation rules, group 1 elements must have an oxidation number of +1.
To balance out the overall charge of zero, the hydrogen in this compound must have an oxidation state of –1. Note that NaH is a metal hydride; therefore, the oxidation state of hydrogen is not necessarily +1.
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
Following the oxidation rules, group 1 elements must have an oxidation number of +1.
To balance out the overall charge of zero, the hydrogen in this compound must have an oxidation state of –1. Note that NaH is a metal hydride; therefore, the oxidation state of hydrogen is not necessarily +1.
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What is the correct oxidation number of zinc in the compound 
?
What is the correct oxidation number of zinc in the compound
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The sum of oxidation numbers of each element in this compound must add to the total charge of -2. Hydrogen always has an oxidation number of +1, and oxygen always has an oxidation number of -2.
So, in total for oxygen we have (4) * (-2) = -8, and for hydrogen we have (4) * (+1) = +4.
Combining the oxygen and hydrogen, (+4) + (-8) = -4, so we need an additional +2 to achieve the total charge of -2. Zn must provide this balancing charge, and have an oxidation number of +2.
The sum of oxidation numbers of each element in this compound must add to the total charge of -2. Hydrogen always has an oxidation number of +1, and oxygen always has an oxidation number of -2.
So, in total for oxygen we have (4) * (-2) = -8, and for hydrogen we have (4) * (+1) = +4.
Combining the oxygen and hydrogen, (+4) + (-8) = -4, so we need an additional +2 to achieve the total charge of -2. Zn must provide this balancing charge, and have an oxidation number of +2.
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Which molecule contains an atom with an oxidation state of 
?
Which molecule contains an atom with an oxidation state of
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The rules for oxidation state note that certain atoms will have constant oxidation values, while others are more likely to vary. Oxygen, for example, will always have an oxidation state of 
, alkali metals will always have an oxidation state of 
, and hydrogen will (almost) always have an oxidation state of 
.
All of the given compounds are neutral, meaning that their oxidation numbers must sum up to zero. Using our listed rules to look at these molecules, we can try to find any missing values.
Chromium in potassium dichromate is the only atom in this set to have an oxidation state of 
.
The rules for oxidation state note that certain atoms will have constant oxidation values, while others are more likely to vary. Oxygen, for example, will always have an oxidation state of
All of the given compounds are neutral, meaning that their oxidation numbers must sum up to zero. Using our listed rules to look at these molecules, we can try to find any missing values.
Chromium in potassium dichromate is the only atom in this set to have an oxidation state of
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Which of the following statements between HClO4 and HClO3 is true?
Which of the following statements between HClO4 and HClO3 is true?
Tap to reveal answer
Oxidation number is a concept that you will also encounter in electrochemistry lectures. It is used to track electrons in an oxidation-reduction reaction. Overall, the sum of the oxidation states of all of the atoms in the molecule must equal the overall charge on the molecule. It is important to remember some of the commonly accepted oxidation states for atoms, so that you can predict the oxidation numbers on other atoms. Here are some key oxidation numbers useful to know for the MCAT:
1. Atoms in elemental form have an oxidation state of 0.
2. Halogens are commonly given an oxidation state of –1.
3. Hydrogen and alkali metals are commonly given an oxidation state of +1.
4. Oxygen is commonly given an oxidation number of –2.
Keeping these rules in mind, we can assume that the hydrogens and oxygens in the two compounds maintain the same oxidation state. Chlorine, however, is attached to one less oxygen in HClO3. As a result, the oxidation state of Cl has decreased from +7 to +5, when comparing HClO4 to HClO3.
Oxidation number is a concept that you will also encounter in electrochemistry lectures. It is used to track electrons in an oxidation-reduction reaction. Overall, the sum of the oxidation states of all of the atoms in the molecule must equal the overall charge on the molecule. It is important to remember some of the commonly accepted oxidation states for atoms, so that you can predict the oxidation numbers on other atoms. Here are some key oxidation numbers useful to know for the MCAT:
1. Atoms in elemental form have an oxidation state of 0.
2. Halogens are commonly given an oxidation state of –1.
3. Hydrogen and alkali metals are commonly given an oxidation state of +1.
4. Oxygen is commonly given an oxidation number of –2.
Keeping these rules in mind, we can assume that the hydrogens and oxygens in the two compounds maintain the same oxidation state. Chlorine, however, is attached to one less oxygen in HClO3. As a result, the oxidation state of Cl has decreased from +7 to +5, when comparing HClO4 to HClO3.
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Which element in the given compounds has the highest oxidation number?
Which element in the given compounds has the highest oxidation number?
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We can calculate the oxidation number in each answer to find the greatest value.
In 
, oxygen will have a value of 
and the molecule is neutral. Sulfur must have an oxidation number of 
to balance the three oxygens.
In 
, oxygen will have a value of 
and the molecule is neutral. Carbon must have an oxidation number of 
to balance the two oxygens.
In 
, chlorine will have a value of 
and the molecule is neutral. Aluminum must have an oxidation number of 
to balance the three chlorines.
In 
, calcium will have a value of 
and the molecule is neutral. Sulfur must have an oxidation number of 
to balance the calcium.
is a molecule comprised of a single element; each atom will have an oxidation number of 
.
We can calculate the oxidation number in each answer to find the greatest value.
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What is the oxidation number of chlorine in the perchlorate ion?
What is the oxidation number of chlorine in the perchlorate ion?
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To find the oxidation number, first remember that the total charge must be preserved. The total charge of the perchlorate ion is 
.
Each oxygen will have an oxidation number of 
. The oxidation of chlorine must be used to balance this negative charge.
To find the oxidation number, first remember that the total charge must be preserved. The total charge of the perchlorate ion is
Each oxygen will have an oxidation number of
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In which of the following compounds does hydrogen have an oxidation number of 
?
In which of the following compounds does hydrogen have an oxidation number of
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Hydrogen generally has an oxidation number of 
in most compounds. The exception is when it is bonded to an alkali metal (group 1 of the periodic table). When hydrogen bonds to one of these elements, it can have an oxidation number of 
. Alkali metals so readily lose their outermost electron that hydrogen must accept it, and thereby acquire a negative charge.
Potassium is an alkali metal, and will have an oxidation number of 
. Hydrogen will balance this by acquiring an oxidation number of 
to keep the molecule neutral. Our answer is 
.
Hydrogen maintains an oxidation number of 
in all other answer options.
Hydrogen generally has an oxidation number of
Potassium is an alkali metal, and will have an oxidation number of
Hydrogen maintains an oxidation number of
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What is the difference in oxidation number between manganese in 
and 
?
What is the difference in oxidation number between manganese in
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The sum of the oxidation numbers of each atom in a molecule must equal the net charge of the molecule.
Oxygen will always have an oxidation number of 
. In 
we can find the oxidation number of manganese with the following equation:
Solving this out, we can see that the charge on manganese must be 
.
In the manganese ions, there is only one atom and the net charge is 
. The oxidation of this manganese atom must be 
to balance the ionic charge.
The difference between these oxidation numbers is:
The sum of the oxidation numbers of each atom in a molecule must equal the net charge of the molecule.
Oxygen will always have an oxidation number of
Solving this out, we can see that the charge on manganese must be
In the manganese ions, there is only one atom and the net charge is
The difference between these oxidation numbers is:
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What is the oxidation number for sulfur in 
?
What is the oxidation number for sulfur in
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The oxidation state of oxygen is always 
, and the oxidation state of magnesium is 
. We know that the oxidation numbers must cancel out to create a neutral molecule.
There are four oxygen atoms, so the total charge from oxygen is 
. If we add 
from the magnesium atom and 
from the oxygen atoms, we get 
. To get the oxidation state of sulfur, we must add a number to 
that totals to zero.
The only number that does this is 
.
The oxidation state of oxygen is always
There are four oxygen atoms, so the total charge from oxygen is
The only number that does this is
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What is the oxidation state of sulfur in H2SO4?
What is the oxidation state of sulfur in H2SO4?
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Since there is no overall charge on the compound the oxidation states must cancel out. Although the oxidation state of hydrides are +1, there are two in the compound that must be accounted for. The same is true for oxygen; although the oxidation number of oxygen is -2, there are four oxygens present accounting for a total of -8. The +2 state contribution from the hydrides and -8 from the oxygens results in a -6 charge. The oxidation state on sulfur must be +6 for the molecule to be neutral.
Since there is no overall charge on the compound the oxidation states must cancel out. Although the oxidation state of hydrides are +1, there are two in the compound that must be accounted for. The same is true for oxygen; although the oxidation number of oxygen is -2, there are four oxygens present accounting for a total of -8. The +2 state contribution from the hydrides and -8 from the oxygens results in a -6 charge. The oxidation state on sulfur must be +6 for the molecule to be neutral.
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What is the correct oxidation number of zinc in the compound ?
What is the correct oxidation number of zinc in the compound
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The sum of oxidation numbers of each element in this compound must add to the total charge of -2. Hydrogen always has an oxidation number of +1, and oxygen always has an oxidation number of -2.
So, in total for oxygen we have (4) * (-2) = -8, and for hydrogen we have (4) * (+1) = +4.
Combining the oxygen and hydrogen, (+4) + (-8) = -4, so we need an additional +2 to achieve the total charge of -2. Zn must provide this balancing charge, and have an oxidation number of +2.
The sum of oxidation numbers of each element in this compound must add to the total charge of -2. Hydrogen always has an oxidation number of +1, and oxygen always has an oxidation number of -2.
So, in total for oxygen we have (4) * (-2) = -8, and for hydrogen we have (4) * (+1) = +4.
Combining the oxygen and hydrogen, (+4) + (-8) = -4, so we need an additional +2 to achieve the total charge of -2. Zn must provide this balancing charge, and have an oxidation number of +2.
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What is the oxidation number of chromium in calcium dichromate (CaCr2O7)?
What is the oxidation number of chromium in calcium dichromate (CaCr2O7)?
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Since the calcium ion has a charge of +2, the dichromate anion must have a charge of -2. Oxygen always has an oxidation number of -2, so the seven oxygens in the molecule have a total number of -14. That leaves a charge of +12 that the two chromiums must balance out (-2 - (-14) = 12). Each chromium must therefore have an oxidation number of +6.
Since the calcium ion has a charge of +2, the dichromate anion must have a charge of -2. Oxygen always has an oxidation number of -2, so the seven oxygens in the molecule have a total number of -14. That leaves a charge of +12 that the two chromiums must balance out (-2 - (-14) = 12). Each chromium must therefore have an oxidation number of +6.
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What is the oxidation state of nitrogen in HNO3?
What is the oxidation state of nitrogen in HNO3?
Tap to reveal answer
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
When applying the oxidation state to HNO3, hydrogen has a +1 oxidation state, and each of the oxygen molecules has a –2 oxidation state. Since there is only one hydrogen molecule and three oxygen molecules, the oxidation state of nitrogen must balance out the charge of the hydrogen molecule and oxygen molecules combined.
Nitrogen must have a +5 oxidation state.
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
When applying the oxidation state to HNO3, hydrogen has a +1 oxidation state, and each of the oxygen molecules has a –2 oxidation state. Since there is only one hydrogen molecule and three oxygen molecules, the oxidation state of nitrogen must balance out the charge of the hydrogen molecule and oxygen molecules combined.
Nitrogen must have a +5 oxidation state.
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What is the oxidation number of hydrogen in NaH?
What is the oxidation number of hydrogen in NaH?
Tap to reveal answer
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
Following the oxidation rules, group 1 elements must have an oxidation number of +1.
To balance out the overall charge of zero, the hydrogen in this compound must have an oxidation state of –1. Note that NaH is a metal hydride; therefore, the oxidation state of hydrogen is not necessarily +1.
When applying oxidation numbers there are certain hierarchical rules that must be followed.
1. The sum of oxidation states of all the elements in a molecule must add up to the overall charge.
2. Group 1 and Group 2 elements have +1 and +2 oxidation states, respectively.
3. Fluorine has an oxidation state of –1.
4. Hydrogen has an oxidation state of +1 (except in metal hydrides).
5. Oxygen has an oxidation state of –2.
6. Elements of the same group (excluding transition metals) generally have the same oxidation state.
Following the oxidation rules, group 1 elements must have an oxidation number of +1.
To balance out the overall charge of zero, the hydrogen in this compound must have an oxidation state of –1. Note that NaH is a metal hydride; therefore, the oxidation state of hydrogen is not necessarily +1.
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Which molecule contains an atom with an oxidation state of ?
Which molecule contains an atom with an oxidation state of
Tap to reveal answer
The rules for oxidation state note that certain atoms will have constant oxidation values, while others are more likely to vary. Oxygen, for example, will always have an oxidation state of , alkali metals will always have an oxidation state of , and hydrogen will (almost) always have an oxidation state of .
All of the given compounds are neutral, meaning that their oxidation numbers must sum up to zero. Using our listed rules to look at these molecules, we can try to find any missing values.
Chromium in potassium dichromate is the only atom in this set to have an oxidation state of .
The rules for oxidation state note that certain atoms will have constant oxidation values, while others are more likely to vary. Oxygen, for example, will always have an oxidation state of
All of the given compounds are neutral, meaning that their oxidation numbers must sum up to zero. Using our listed rules to look at these molecules, we can try to find any missing values.
Chromium in potassium dichromate is the only atom in this set to have an oxidation state of
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Which of the following statements between HClO4 and HClO3 is true?
Which of the following statements between HClO4 and HClO3 is true?
Tap to reveal answer
Oxidation number is a concept that you will also encounter in electrochemistry lectures. It is used to track electrons in an oxidation-reduction reaction. Overall, the sum of the oxidation states of all of the atoms in the molecule must equal the overall charge on the molecule. It is important to remember some of the commonly accepted oxidation states for atoms, so that you can predict the oxidation numbers on other atoms. Here are some key oxidation numbers useful to know for the MCAT:
1. Atoms in elemental form have an oxidation state of 0.
2. Halogens are commonly given an oxidation state of –1.
3. Hydrogen and alkali metals are commonly given an oxidation state of +1.
4. Oxygen is commonly given an oxidation number of –2.
Keeping these rules in mind, we can assume that the hydrogens and oxygens in the two compounds maintain the same oxidation state. Chlorine, however, is attached to one less oxygen in HClO3. As a result, the oxidation state of Cl has decreased from +7 to +5, when comparing HClO4 to HClO3.
Oxidation number is a concept that you will also encounter in electrochemistry lectures. It is used to track electrons in an oxidation-reduction reaction. Overall, the sum of the oxidation states of all of the atoms in the molecule must equal the overall charge on the molecule. It is important to remember some of the commonly accepted oxidation states for atoms, so that you can predict the oxidation numbers on other atoms. Here are some key oxidation numbers useful to know for the MCAT:
1. Atoms in elemental form have an oxidation state of 0.
2. Halogens are commonly given an oxidation state of –1.
3. Hydrogen and alkali metals are commonly given an oxidation state of +1.
4. Oxygen is commonly given an oxidation number of –2.
Keeping these rules in mind, we can assume that the hydrogens and oxygens in the two compounds maintain the same oxidation state. Chlorine, however, is attached to one less oxygen in HClO3. As a result, the oxidation state of Cl has decreased from +7 to +5, when comparing HClO4 to HClO3.
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Which element in the given compounds has the highest oxidation number?
Which element in the given compounds has the highest oxidation number?
Tap to reveal answer
We can calculate the oxidation number in each answer to find the greatest value.
In , oxygen will have a value of and the molecule is neutral. Sulfur must have an oxidation number of to balance the three oxygens.
In , oxygen will have a value of and the molecule is neutral. Carbon must have an oxidation number of to balance the two oxygens.
In , chlorine will have a value of and the molecule is neutral. Aluminum must have an oxidation number of to balance the three chlorines.
In , calcium will have a value of and the molecule is neutral. Sulfur must have an oxidation number of to balance the calcium.
is a molecule comprised of a single element; each atom will have an oxidation number of .
We can calculate the oxidation number in each answer to find the greatest value.
In
In
In
In
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