Alkali metals have negative reduction potential and hence they behave as

Which one of the following statements is correct?

The metal that forms nitride by reacting directly with $N_2$ of air is

Statement $I$: An alloy of lithium and magnesium is used to make aircraft plates.
Statement $II$: The magnesium ions are important for cell-membrane integrity.
In the light of the above statements,choose the correct answer from the options given below.

Which of the following $s$-block elements forms a nitride directly by reacting with $N_2$?

$Na_2CO_3$ is prepared by the Solvay process,but $K_2CO_3$ cannot be prepared by the same process because: