Question

Which of the following reactions are comproportionation reactions?

• A. $2H_{2}S\left(g\right)+S{O}_2\left(g\right)\to 3S\left(s\right)+2H_{2}O\left(g\right)$
• B. $2A{g}^{2+}\left(aq\right)+Ag\left(s\right)\to 2A{g}^{+}\left(g\right)$
• C. $CaC{O}_3\left(s\right)\stackrel{\Delta }{\to }CaO\left(s\right)+C{O}_2\left(g\right)$
• D. $H_2\left(g\right)+I_2\left(g\right)\to 2HI\left(g\right)$

Answer 1

Answer: (A), (B)

The correct options are
A $2H_{2}S\left(g\right)+S{O}_2\left(g\right)\to 3S\left(s\right)+2H_{2}O\left(g\right)$
B $2A{g}^{2+}\left(aq\right)+Ag\left(s\right)\to 2A{g}^{+}\left(g\right)$

A reaction in which an element in a higher oxidation state reacts with the same element in a lower oxidation state to give the element in an intermediate oxidation state is known as comproportionation or symproportionation.
In option A:
$2H_2\stackrel{-2}{S}\left(g\right)+\stackrel{+4}{S}{O}_2\left(g\right)\to 3\stackrel{0}{S}\left(s\right)+2H_{2}O\left(g\right)$
Sulphur in $-2$ and $+4$ oxidation states changes to $0$ oxidation state.
In option B:
$2A{g}^{2+}\left(aq\right)+\stackrel{0}{A}g\left(s\right)\to 2A{g}^{+}\left(g\right)$
Here silver in $+2$ and $0$ states changes to $+1$ state.