Question

In the following reactions:
$AlC{l}_3+3K\to Al+3KCl$
$S{O}_2+2H_{2}S\to 3S+H_{2}O$
$3I_2+6NaOH\to NaI{O}_3+5NaI+3H_{2}O$
Identify the correct option which represents the oxidised substances?

• A. $K,S{O}_2,I_2$
• B. $K,H_{2}S,I_2$
• C. $AlC{l}_3,H_{2}S,I_2$
• D. $AlC{l}_3,S{O}_2,I_2$

Answer 1

Answer: (B)

$K,H_{2}S,I_2$

(i) $A{l}^{3+}\to A{l}^0$ and $K^0\to K^{+}$
Thus, $A{l}^{3+}$ is reduced and $K$ is oxidised.
Note : The atom having higher oxidation number in a conjugate redox pair is oxidant and is therefore reduced.
(ii) Similarly, $S{O}_2$ is reduced and $H_{2}S$ is oxidised.
(iii) Similarly, neither one is reduced nor one is oxidised ($\because$ No change in oxidation number during reaction).
(iv) $I_2$ is itself oxidised as well as reduced.
$I_2^0\to 2I^{5+}+10e$
$2e+I_2^0\to 2I^{-}$