Which of the following reaction of diazonium salt involves retention of diazonium group?

Identify compound '$$B$$' in following series of reactions?

$$\text { Acetonitrile } \xrightarrow{\mathrm{Na} / \text { alcohol }} A \xrightarrow{\mathrm{NaNO}_2 / \text { dil. } \mathrm{HCl}} B$$

Identify the product '$$A$$' in the following reaction.

$$\text { Aniline } \xrightarrow[\text { Pyridine }]{\left(\mathrm{CH}_3 \mathrm{CO}\right)_2 \mathrm{O}} A$$

Alkyl cynides on reduction by sodium and ethanol give primary amines. This reaction is called as