What is the action of the sodium metal in ammonia?

Metal made of sodium is very reactive. Ammonia is quite heated and light stable, although it reacts very quickly with oxidizing gases. Displacement reaction is the sort of reaction. When sodium, an alkali metal, comes into touch with water or air, it becomes very reactive. Thus, it is preserved by submerging in kerosene. But when it interacts with water to generate sodium hydroxide, it functions as a potent base. A basic, ammonia reacts angrily with acids. It is explosively reactive toward reducing substances and forms its compounds by reacting with silver and mercury. In a slow reactivity range at room temperature, sodium and ammonia combine to form sodium amide, which releases hydrogen in the process.

Sodium is a highly reactive metal. The reaction between sodium and ammonia is as follows

$2\mathrm{Na}+2{\mathrm{NH}}_3\to 2{\mathrm{NaNH}}_2+{\mathrm{H}}_2$

As a result sodium amide and hydrogen is produced.

Hence, option B is correct.