Question

Which among the following are intramolecular redox reactions?

• A. $P{Cl}_5⟶P{Cl}_3+{Cl}_2$
• B. $CHO-CHO+O{H}^{-}\to CO{O}^{-}-C{H}_{2}OH$
• C. $2KCl{O}_3⟶2KCl+3O_2$
• D. ${NH}_{4}N{O}_2⟶N_2+2H_{2}O$

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A $P{Cl}_5⟶P{Cl}_3+{Cl}_2$
B $CHO-CHO+O{H}^{-}\to CO{O}^{-}-C{H}_{2}OH$
C $2KCl{O}_3⟶2KCl+3O_2$
D ${NH}_{4}N{O}_2⟶N_2+2H_{2}O$

(a) $\underset{\uparrow +5}{P}\underset{\uparrow -1}{{Cl}_5}⟶\underset{\uparrow +3}{P}{Cl}_3+\underset{\uparrow 0}{{Cl}_2}$

(c) $2K\underset{\uparrow +5}{Cl}\underset{\uparrow -2}{O_3}⟶\underset{\uparrow -1}{KCl}+\underset{\uparrow 0}{O_2}$

(d) $\underset{\uparrow -3}{{NH}_4}\underset{\uparrow +4}{N}{O}_2⟶\underset{0}{N_2}$

The decomposition of phosphorus pentachloride is intramolecular redox reaction. In this reaction, the oxidation number of phosphorus changes from +5 to +3 and the oxidation number of chlorine changes from -1 to 0. Thus, phosphorus is reduced and chlorine is oxidized. Thus, the option A is correct.

The reaction of option (B) is an example of base introduced intramolecular disproportionation reaction also known as cannizzaro reaction. In this reaction, one aldehyde group is oxidized to carboxylic group and other aldehyde group is reduced to alcoholic -OH group. Thus it is an intramolecular redox reaction.

In the reaction of option (C), the oxidation number of chlorine changes from +5 to -1 and the oxidation number of oxygen changes from -2 to 0. Thus, chlorine is reduced and oxygen is oxidized. Hence, it is an intramolecular redox reaction. Thus, option (C) is correct.

In the reaction (D), the oxidation number of the nitrogen atom of ammonium group changes from -3 to 0. Thus, it is oxidized. The oxidation number of the nitrogen of nitro group changes from +4 to 0. Thus, it is reduced. Hence, this is an example of intramolecular redox reaction. Thus, the option (D) is also correct.