Explanation

(a)
Caro’s acid is $H_{2}{SO}_{5}.$ It has a peroxide linkage so, oxidation state of S is
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Let the oxidation state of S is $x.$
$H_{2}{SO}_{5}(one\ peroxide\ bond)$
$+ 2 + x + 3( - 2) + 1( - 2) = 0$
$2 + x - 6 - 2 = 0$
$x - 6 = 0$
$x = 6$