Which of the following molecular formula represents Marshall's acid?

An element crystallises in fcc type of unit cell. The volume of one unit cell is $24.99 \times 10^{-24} \mathrm{~cm}^3$ and density of the element $7.2 \mathrm{~g} \mathrm{~cm}^{-3}$. Calculate the number of unit cells in 36 g of pure sample of element?

Which of the following reagents is used for the following conversion?

$$\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CHO} \longrightarrow \mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2 \mathrm{OH}$$

Identify $A$ in the following reaction.

$$A+\mathrm{CH}_3 \mathrm{MgBr} \xrightarrow{\text { Ether }} \text { complex }\xrightarrow{\mathrm{H}_3 \mathrm{O}^{+}}\left(\mathrm{CH}_3\right)_3 \mathrm{C}-\mathrm{OH}$$