Explanation

(b)
In presence of slight amount of a dil acid, bleaching powder loses oxygen. Due to this nascent oxygen, it shows oxidizing and bleaching properties,
$2CaOCl_{2} + H_{2}SO_{4} \rightarrow CaCl_{2} + CaSO_{4} + 2HClO$
$HClO \rightarrow HCl + \lbrack O\rbrack$