Explanation

(a)
$K_{2}\left( SO_{4} \right).Al_{2}\left( SO_{4} \right)_{3}.24H_{2}O$ gives
$\ \ \ \ \ \ \ \ \ \ K_{2}SO_{4} + Al_{2}\left( SO_{4} \right)_{3} + 24H_{2}O$
$Al_{2}\left( SO_{4} \right)_{3}$ undergoes hydrolysis to give $H_{2}SO_{4}$
$Al_{2}\left( SO_{4} \right)_{3} + 6H_{2}O \rightarrow 2Al(OH)_{3} + 3H_{2}SO_{4}$
due to which aqueous solution of potash alum is acidic.