Explanation

(d)
$CH_{3}CH_{2}C \equiv CH + H_{2}O\overset{\frac{HgSO_{4}}{H_{2}SO_{4}}}{\rightarrow}$
1-butyne
$OH$ $OH$
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$CH_{3}CH_{2}C = CH_{2}\overset{H_{2}O}{\rightarrow}CH_{3}CH_{2} - C - CH_{3}$
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$OH$
unstable
$\overset{- H_{2}O}{\rightarrow}CH_{3}CH_{2} - C - CH_{3}$
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$O$
butan-2-one