Balance the following disproportionation reaction: KIO₂ ⇌ KI + KIO₃
A) 3 KIO₂ ⇌ 2 KI + KIO₃
B) 4 KIO₂ ⇌ 3 KI + KIO₃
C) 5 KIO₂ ⇌ 3 KI + 2 KIO₃
D) 4 KIO₂ ⇌ 2 KI + KIO₃
E) 3 KIO₂ ⇌ KI + 2 KIO₃
IMAT 2026 · Question 40
Q40 - Oxidation and reduction
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The correct answer is E) 3 KIO₂ ⇌ KI + 2 KIO₃.
In a disproportionation, the same element is both oxidised and reduced. Here it is iodine.
Oxidation numbers (K = +1, O = −2):
KIO₂: I = +3
KI: I = −1, so going to KI it gains 4 e⁻
KIO₃: I = +5, so going to KIO₃ it loses 2 e⁻
For electrons to balance, each KI (4 e⁻ gained) needs 2 KIO₃ (2 × 2 e⁻ lost). That uses 3 iodine atoms, so 3 KIO₂.
Check: K 3 = 1 + 2; I 3 = 1 + 2; O 6 = 0 + 6. Balanced.
Options A–D all fail the electron balance (or the oxygen count).
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