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Oxidation State Questions

Oxidation state is a theoretical concept. It tells us about the number of electrons gained, lost or shared by the transition metal atom. It is the average value and can be positive, negative or fractional.

Definition: The oxidation state tells us about the degree of oxidation, i.e. the number of electrons gained, lost, or shared.

Oxidation State Chemistry Questions with Solutions

Q1. What is the oxidation state of chromium in K2CrO4?

  1. + 6
  2. + 5
  3. + 7
  4. None of the above

Answer: (a), The oxidation state of chromium in K2CrO4 is + 6.

Calculation:

1 X 2 + x + 4 X (- 2) = 0

2 + x – 8 = 0

x – 6 = 0

x = + 6

Hence, the oxidation state of chromium in K2CrO4 is + 6.

Q2. What is the oxidation state of iron in Fe(CO)5?

  1. – 1
  2. 0
  3. + 1
  4. None of the above

Answer: (b), The oxidation state of iron in Fe(CO)5 is zero.

Calculation:

x + 5 X 0 = 0

x = 0

Hence, the oxidation state of iron in Fe(CO)5 is zero.

Q3. What is the oxidation state of oxygen in the ozone?

  1. 0
  2. + 1
  3. + 2
  4. + 3
  5. None of the above

Answer: (a), The oxidation state of oxygen in the ozone is zero.

Explanation: The ozone molecule comprises three oxygen atoms bonded together in elemental form. Since no electrons are transferred in the atom’s elemental form, thus, the oxidation state of oxygen in the ozone is equivalent to zero.

Q4. In which of the following compound will chlorine show the highest oxidation state?

  1. HCl
  2. HClO4
  3. KClO3
  4. None of the above

Answer: (b), Chlorine will show the highest oxidation state in HClO4.

Explanation: To understand it better, first, we will calculate the oxidation state of HCl, HClO4, and KClO3.

The oxidation state of chlorine in HCl will be

1 + x = 0

x = – 1

The oxidation state of chlorine in HClO4 will be:

1 + x + 4 X ( -2) = 0

1 + x – 8 = 0

x – 7 = 0

x = + 7

The oxidation state of chlorine in KClO3 will be

1 + x + 3 X ( -2 ) = 0

1 + x – 6 = 0

x = + 5

Hence the oxidation state of chlorine is maximum in HClO4, i.e. equivalent to + 7.

Q5. The oxidation state of an element tells us about the

  1. Number of electrons gained
  2. Number of electrons lost
  3. Number of electrons shared
  4. Degree of oxidation
  5. All of the above

Answer: (e), The oxidation state of an element tells us about the number of electrons gained, lost, or shared, i.e. degree of oxidation of an element.

Q6. The oxidation number of an element tells us about the

  1. Charge on the central metal atom
  2. Number of electrons gained, lost or shared
  3. Degree of oxidation
  4. All of the above
  5. None of the above

Answer: (a), The oxidation number of an element tells us about the charge on the central metal atom even after all the ligands are removed.

Q7. What is the oxidation state of platinum in [PtCl6]2-

  1. + 2
  2. + 4
  3. + 6
  4. None of the above

Answer: (b), The oxidation state of platinum in [PtCl6]2- is + 4.

Calculation:

x + 6 X – 1 = – 2

x – 6 = – 2

x = 6 – 2

x = + 4

Hence, the oxidation state of platinum in [PtCl6]2- is + 4.

Q8. What is the oxidation state of iron in [Fe(H2O)6] 2+

  1. + 2
  2. + 4
  3. + 6
  4. + 8

Answer: (a), The oxidation state of iron in [Fe(H2O)6] 2+ is + 2.

Calculation:

x + 6 X 0 = + 2

x = + 2

Hence, the oxidation state of iron in [Fe(H2O)6] 2+ is + 2.

Q9. What is the oxidation state of cobalt in [CoCl6]2-

  1. + 2
  2. + 4
  3. + 6
  4. None of the above

Answer: (b), The oxidation state of cobalt in [CoCl6]2- is + 4.

Calculation:

x + 6 X – 1 = – 2

x – 6 = – 2

x = 6 – 2

x = + 4

Hence, the oxidation state of cobalt in [CoCl6]2- is + 4.

Q10. What is the oxidation state of platinum in [V (H2O)6] 3+

  1. + 3
  2. + 4
  3. + 5
  4. None of the above

Answer: (a), The oxidation state of vanadium in [V (H2O)6] 3+ is + 3.

Calculation:

x + 6 X 0 = + 3

x = + 3

Hence, the oxidation state of vanadium in [V (H2O)6] 3+ is + 3.

Q11. Are the oxidation state and the oxidation number the same?

Answer: No, the oxidation state and the oxidation number are not the same. The oxidation state tells us about the degree of oxidation, i.e. the number of electrons gained, lost, or shared. In contrast, the oxidation number tells us about the charge on the central metal atom even after all the ligands are removed.

Q12. Name an element that shows a negative oxidation state only.

  1. Fluorine
  2. Oxygen
  3. Nitrogen
  4. None of the above

Answer: (a), Fluorine is the most electronegative element. It shows a negative oxidation state only.

Q13. The oxidation state of nitrogen in NO4+ is

  1. + 5
  2. + 7
  3. + 9
  4. None of the above

Answer: ( c), The oxidation state of nitrogen in NO4+ is + 9.

Calculation:

x + 4 X ( – 2 ) = 1

x – 8 = 1

x = + 9

Hence, the oxidation state of nitrogen in NO4+ is is + 9.

Q14. Match the following.

Column 1

Column 2

Ions with a positive charge

( + 2 )

Ions with a negative charge

( + 1 )

The sum of oxidation states of all atoms in a neutral molecule is

( – 1 )

Oxidation state of hydrogen ion (H+)

0

Oxidation state of fluorine in

NaF

Anion

The oxidation state of oxygen in OF2

Cation

Answer:

Column 1

Column 2

Ions with a positive charge

Cation

Ions with a negative charge

Anion

The sum of oxidation states of all atoms in a neutral molecule is

0

Oxidation state of hydrogen ion (H+)

( + 1 )

Oxidation state of fluorine in

NaF

( – 1 )

The oxidation state of oxygen in OF2

( + 2 )

Q15. Distinguish between oxidation state and oxidation number.

Answer:

S. No.

Oxidation state

Oxidation number

1.

The oxidation state tells us about the degree of oxidation, i.e. the number of electrons gained, lost, or shared.

The oxidation number tells us about the charge on the central metal atom even after all the ligands are removed.

2.

It does not tell us about the charge on the central atom.

It tells us about the charge on the central atom.

Practise Questions on Oxidation State

Q1. What are the rules for finding oxidation states?

Q2. In bleaching powder (CaOCl2), the oxidation state of the two chlorine atoms is

  1. 0, + 1
  2. + 1, + 2
  3. 0, – 1
  4. – 1, + 1

Q3. Why does fluorine show a negative oxidation state only?

Q4. How many electrons are involved in the following redox reaction?

Cr2O72- + Fe2+ + C2O42- → Cr3+ + Fe3+ + CO2

Note: The equation is not balanced.

Q5. What are the oxidation states and the covalency of sulphur molecule in S8?

  1. 0, 2
  2. 0, 4
  3. 0, 6
  4. None of the above

Click the PDF to check the answers for Practice Questions.
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