# Bleaching action of $SO_2$ due to

$\begin{array}{1 1}(a)\;Oxidising\;action\\(b)\;Acidic\;Nature\\(c)\;Ability\;hydrolyse\\(d)\;Reducing\;action\end{array}$

$SO_2+2H_2O\rightarrow H_2SO_4+2[H]$
$2[H]+colour\rightarrow$ colourless
The bleaching powder is due to n oscent hydrogen is reducing agent.
Hence (d) is the correct answer.