Identify the product ' B ' in the following sequence of recations.

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

Which of the following elements belongs to second group and fifth period of periodic table?

Which among the following has lowest boiling point?

Which of the following species contain 20 electrons?