Identify ' B ' in the following conversion.

$$\mathrm{CH}_3-\mathrm{I} \xrightarrow{\mathrm{KCN}} \mathrm{~A} \xrightarrow{\mathrm{Na} / \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}} \mathrm{~B}$$

What is the number of lone pair of electrons on central halogen atom in BrF$_3$?

One mole of a gas occupying 3 L volume is expanded against a constant external pressure of 1 bar to a volume of 15 L . Calculate work done by the system

Calculate $\Delta \mathrm{T}_{\mathrm{f}}$ of aqueous 0.01 m formic acid if van't Hoff factor is 1.1

$$\left[\mathrm{K}_{\mathrm{f}}=1.86 \mathrm{~K} \mathrm{~Kg} \mathrm{~mol}^{-1}\right]$$