The best reagent to convert pent$ - 3 - en - 2 - ol$ and pent$ - 3 - en - 2 - one$ is:
A.Acidic permanganate
B.Acidic dichromate
C.Chromic anhydride in glacial acetic acid
D.Pyridinium chlorochromate

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Hint: At first think about the reagents which convert the alcohol to a ketone. The reaction of alcohol to a ketone is nothing but oxidation of alcohol. Oxidation of alcohol is also known as dehydrogenation reaction.

Complete step by step answer:
The structures of pent$ - 3 - en - 2 - ol$and pent$ - 3 - en - 2 - one$ are
$C{H_3} - CH = CH - CH(OH) - C{H_3}$and $C{H_3} - CH = CH - CH(O) - C{H_3}$ respectively.
From the above structure, we can say that alcohol is a tertiary alcohol. The tertiary alcohol does not undergo oxidation due to a lack of $\alpha $ hydrogen.
The reagent acidic permanganate is used for the oxidation of primary alcohols to carboxylic acids. So it is incorrect.
The reagent acidic dichromate is used for the oxidation of primary alcohols to carboxylic acids, secondary alcohols to ketones and for tertiary alcohol, there is no reaction.
The chromic anhydride in glacial acetic acid is a strong oxidizing agent. It can convert tertiary alcohol to ketone but it can affect other atoms.
Pyridinium chlorochromate (PCC) is a mild oxidizing agent so without affecting the other atoms it can convert tertiary alcohol to a ketone. Although acidic permanganate, acidic dichromate, and chromic anhydride in glacial acetic acid are strong oxidizing agents, the PCC is best suitable to convert tertiary alcohol to a ketone.
So the answer is D.
Note:
Strong oxidizing agents can be easily suitable for the oxidation of alcohol but due to their strong nature, it may affect other atoms. Mild oxidizing agents cannot affect the other atoms as their action is less.