Which of the following reagent is used to convert alkene to alcohol...

Hydration of alkenes to alcohols requires the addition of water across the carbon-carbon double bond.

Since water is a weak acid, it cannot initiate the electrophilic addition reaction on its own. An acid catalyst is required to provide $\text{H}^+$ ions, which attack the double bond to form a carbocation intermediate.

Therefore, $\text{H}_2\text{O}$ in the presence of a strong acid like $\text{H}_2\text{SO}_4$ (dilute sulfuric acid) is used as the reagent for the hydration of alkenes to yield alcohols.

Answer: $\text{H}_2\text{O}$ in presence of $\text{H}_2\text{SO}_4$