Which of the following methods is used to prepare dihydrogen with purity greater than 99.5 ?

Cyclohexene on oxidation with $\mathrm{KMnO}_4$ in dil. $\mathrm{H}_2 \mathrm{SO}_4$ forms

Calculate the enthalpy change of vaporisation of benzene if 13 gram of benzene vaporised by supplying 5.1 kJ of heat.

The volume of simple unit cell is $x \times 10^{-23} \mathrm{~cm}^3$. Calculate the value of $x$ if volume occupied by a particle in it is $2.1 \times 10^{-23} \mathrm{~cm}^3$.