MCQs on Oxidation Number and Oxidation State

Oxidation state is a fundamental concept in chemistry, and is particularly important in transition metal chemistry, as d-block elements often have a wide range of stable oxidation states. The oxidation state (number) of an atom within a molecule is usually considered to be the formal charge on the atom if hypothetically all of the molecules are composed of ions. Oxidation numbers assigned to atoms in a rather arbitrary fashion to designate electron transfer in oxidation-reduction reactions. They represent the charges that atoms would have if the electrons were assigned according to an arbitrary set of rules. According to IUPAC, the oxidation state of the element is defined as a measure of the degree of oxidation of an atom in a substance.

1. Number of moles of K2Cr2O7 reduced by 1 mole of Sn2+ is

  1. 1/6
  2. 1/3
  3. 2/3
  4. 1

Answer: (b)

2. The oxidation number of carbon in CH2Cl2 is

  1. 0
  2. 2
  3. 3
  4. 5

Answer: (a)

3. Which of the following will not be oxidised by O3?

  1. KI
  2. FeSO4
  3. KMnO4
  4. K2MnO4

Answer: (c)

4. The oxidation state of chromium in the final product formed by the reaction between KI and acidified potassium dichromate solution is

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

Answer: (d)

5. What products are expected from the disproportionation reaction of hypochlorous acid?

  1. HCl and Cl2O
  2. HCl and HClO3
  3. HClO3 and Cl2O
  4. HClO2 and HClO4

Answer: (b)

6. Which of the following elements does not show disproportionation tendency?

  1. Cl
  2. Br
  3. F
  4. I

Answer: (c)

7. What is the oxidation number of chlorine in HClO4?

  1. +3
  2. +5
  3. +7
  4. +8

Answer: (c)

8. The oxidation state of each Cl in CaOCl2 is

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

Answer: (d)

9. The products formed when an aqueous solution of NaBr is electrolysed in a cell having inert electrodes are

  1. Na and Br2
  2. Na and O2
  3. H2, Br2, NaOH
  4. H2 and O2

Answer: (c)

10. Number of moles of MnO4 required to oxidise one mole of ferrous oxalate completely in the acidic medium will be

  1. 7.5 moles
  2. 0.2 moles
  3. 0.6 moles
  4. 0.4 moles

Answer: (c)

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