In which of the following compounds, the oxidation number of iodine is fractional ?

IF₇
\(I_{3}^{-}\)
IF₅(d)
IF₃

Solution

O.N. of iodine in \(I_{3}^{-}\) is –1/3.

In the reaction
Ag₂O + H₂O₂ ⟶ 2Ag + H₂O + O₂, the H₂O₂ acts as :

reducing agent
oxidising agent
bleaching agent
none of the above

Solution

H₂O₂ is converting Ag₂O into Ag,so it is reducing Ag₂O. Hence it is a reducing agent here.

In which of the following transition metal complexes does the metal exhibit zero oxidation state ?

[Co(NH₃)₆]Cl₃
[Fe(H₂O₆]SO₄
Ni(CO)₄
[Fe(H₂O₆]X₃

Solution

In metal carbonyls metal always has O.N. zero.

When SO₂ is passed through acidified solution of potassium dichromate, then chromium sulphate is formed. The change in valency of chromium is

+4 to +2
+5 to +3
+6 to +3
+7 to +2

Solution

In which of the following compounds the oxidation number of carbon is not zero?

HCHO
CH₃COOH
C₁₂H₂₂O₁₁
CH₃CHO

Solution

O.N. of carbon in CH₃CHO is –1; in other cases it is zero.

The values of standard oxidation potentials of following reactions are given below :
(i)Zn ⟶ Zn²⁺ + 2e^–; Eº = 0.762V
(i)Fe ⟶ Fe²⁺ + 2e^–; Eº = 0.440V
(i)Cu ⟶ Cu²⁺ + 2e^–; Eº = -0.345V
(i)Ag ⟶ Ag⁺ + e^–; Eº = -0.800V
Which of the following is most easily reduced

Solution

As the oxidation potential of Ag is the lowest among the given elements, hence it would be reduced most readily.

Among the following, identify the species with an atom in+6 oxidation state

\(MnO_{4}^{-}\)
\(Cr(CN)_{6}^{3-}\)
\(NiF_{6}^{2-}\)
CrO₂Cl₂

Solution

\(MnO_{4}^{-}\) (O.S. of Mn +7); \(Cr(CN)_{6}^{3-}\)(O.S. of Cr+3), \(NiF_{6}^{2-}\)(O.S. of Ni +4) and CrO₂Cl₂ (O.S. of Cr +6).

On reduction of KMnO₄ by oxalic acid in acidic medium, the oxidation number of Mn changes. What is the magnitude of this change?

From 7 to 2
From 6 to 2
From 5 to 2
From 7 to 4

Solution

In acidic medium \(MnO_{4}^{-}\) changes to Mn²⁺, hence O.N.changes from +7 to +2.

In which of the compounds does ‘manganese’ exhibit highest oxidation number ?

MnO₂
Mn₃O₄
K₂MnO₄
MnSO₄

Solution

O.N. of Mn in K₂MnO₄ is +6

H₂C₂O₄ + KMnO₄ in acidic medium reacts to have change in oxidation number of Mn from :

7 to 5
2 to 7
5 to 7
7 to 2

Solution

\(MnO_{4}^{-}\) changes to Mn²⁺

\(MnO_{4}^{-}\) + 8H⁺ + 5e = Mn²⁺ + 4H₂O
Oxidation No of Mn charges from +7 to + 2

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