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.

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.

Answer:

Q15. Distinguish between oxidation state and oxidation number.

Answer:

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?

Cr₂O₇^2- + Fe²⁺ + C₂O₄^2- → 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

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