Cyclohexene on reaction with OsO₄ followed by reaction with NaHSO₃ gives
A. Cis-diol
B. Trans-diol
C. Epoxy
D. Alcohol

Hint: The process of conversion of alkene into vicinal diol is called dihydroxylation. It is an oxidation process and for this process, a transition metal with a high oxidation state is needed like osmium or manganese. OsO₄ is the most important oxidising agent which is used for the process of dihydroxylation.

Complete Step by Step Answer:
The reaction of cyclohexane with OsO₄ is a dihydroxylation reaction, dihydroxylation means the addition of two hydroxyl groups in the substituent, and the formation of vicinal diol takes place.

The reaction of Cyclohexene with OsO4 followed by a reaction with NaHSO₃ will give a diol-
$C_6H_{10}\xrightarrow[]{OsO_4/NaHSO_3}C_6H_{10}\left ( OH \right )_2$


This is an oxidative addition reaction. And the mechanism of the reaction passes through the transition state and the formation of the transition state requires syn addition thus the product formed will be syn.
The reaction mechanism is

This process follows no rearrangement. The reaction follows syn addition, that is the addition of a new bond will be at the same face of the reactant. In this reaction, NaHSO₃ is used to break the five-membered cyclic transition state.
Thus we can see that the Cyclohexene on reaction with OsO₄ followed by reaction with NaHSO₃ gives cyclohexane cis diol.
Thus, Option (A) is correct

Note: Bayer’s reagent which is alkaline potassium permanganate (alkaline) KMnO₄ is also a strong oxidising agent which is also used for the formation of vicinal diol. Manganese also has a high oxidation state. It is also used for the determination of unsaturation in a compound.