Oxidation number of N in HNO₂ is :

–3.5
+3.5
–5
+5

Solution

Let the oxidation no. of N in HNO₃ = x

∴ 1 + x + (3 × –2) = 0

∴ x = +5

When Sn²⁺ changes to Sn⁴⁺ in a reaction

It loses two electrons
It gains two electrons
It loses two protons
It gains two protons

Solution

Sn²⁺ → Sn²⁺ + 2e^-.

In this reaction Sn²⁺ change in Sn⁴⁺ it is called an oxidation reaction.

The conversion of sugar C₁₂H₂₂O₁₁ → CO₂ is

oxidation
reduction
Both oxidation and reduction
Neither oxidation nor reduction

Solution

In this reaction oxidation occur.

The element that is easiest to be reduced:

Solution

Ag is easiest to be reduced among the given choices because its reduction potential is highest among the given choices.

In the reaction 3Mg + N₂ → Mg₃N₂

magnesium is reduced
magnesium is oxidized
nitrogen is oxidized
None of these

Solution

In the given reaction oxidation state of Mg is changing from 0 to +2 while in nitrogen it is changing from 0 to –3.

So oxidation of Mg and reduction of nitrogen takes place.

H₂S acts only as a reducing agent while SO₂ can act both as a reducing and oxidizing agent because

oxygen is more – ve in SO₂
hydrogen in H₂S is more +ve than oxygen
S in SO₂ has one oxidation state
S in H₂S has –2 oxidation state

Solution

H₂S, the oxidation state of S is –2.

So it cannot accept more electrons because on accepting 2 electrons S accquires a noble gas configuration.

So, it can acts only as a reducing agent by loosing electron.

On the other hand, the oxidation state of S in SO₂ is +4 which is an intermediate oxidation state of sulphur so it can reduce as well oxidise.

In the following reaction

4P + 3KOH + 3H₂O → 3KH₂PO₂ + PH₃

phosphorus is both oxidised and reduced.
only phosphorus is reduced.
phosphorus is not oxidised
None of these

Solution

4P + 3KOH + 3H₂O → 3KH₂PO₂ + PH₃

O.N of P = 0, In KH₂PO₂ it is + 1, In PH₃ it is -3.

Hence P is oxidised and reduced.

Which reaction involves neither oxidation nor reduction?

CrO₄^2- → Cr₂O₇^2-
Cr → CrCl₃
Na → Na⁺
2S₂O₃^2- → S₄O₆^2-

Solution

Ox. no. of Cr on both side is +6.

The standard reduction potential of Li⁺/Li, Ba²⁺/Ba, Na⁺/Na and Mg²⁺/Mg are – 3.05, – 2.73, –2.71 and – 2.37 volts respectively. Which one of the following is strongest oxidising agent?

Li⁺
Na⁺
Mg²⁺
Ba²⁺

Solution

Higher values of reduction potential indicates the stronger oxidising agent.

So, Mg²⁺ having reduction potential –2.37 V, is the strongest oxidising agent among the given choices.

Which of the following involves transfer of five electrons ?

MnO₄^- → Mn²⁺
CrO₄^2- → Cr³⁺
MnO₄^2- → MnO₂
Cr₂O₇^2- → 2Cr³⁺

Solution

O.N. of Mn in MnO₄^- is +7 and in Mn²⁺ it is +2.

The difference is of 5 electrons.

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