A hydrocarbon X, C5H8, gives a white precipitate with ammoniacal AgNO3 and on catalytic hydrogenation with excess H2 gives 2-methylbutane. Hydration of X with HgSO4 / dilute H2SO4 gives mainly

JEE Advanced levelSingle correct optionDifficulty 3 of 3hc126

A hydrocarbon X, $C X_{5} H X_{8}$ , gives a white precipitate with ammoniacal $AgNO X_{3}$ and on catalytic hydrogenation with excess $H X_{2}$ gives 2-methylbutane. Hydration of X with $HgSO X_{4}$ / dilute $H X_{2} SO X_{4}$ gives mainly

The precipitate shows a terminal alkyne and the hydrogenation product fixes the skeleton, so X is 3-methylbut-1-yne,

(CH X_{3}) X_{2} CH - C \equiv CH

. Markovnikov hydration places oxygen on the internal carbon: enol tautomerises to

(CH X_{3}) X_{2} CH - CO - CH X_{3}

, 3-methylbutan-2-one.