The stability of the following alkali metal chlorides follows the order:

$A$ metal $M$ reacts with $N_2$ to form a compound $A$ $(M_3N)$. Heating $A$ at a high temperature gives back $M$,and passing $A$ through $H_2O$ results in the evolution of gas $B$. Gas $B$ turns $CuSO_4$ solution blue. What are $A$ and $B$ respectively?

By which method can the concentration of alkali metals be determined?

Which of the following is an alkali metal?

The reaction of an element $A$ with water produces a combustible gas $B$ and an aqueous solution of $C.$ When another substance $D$ reacts with this solution $C,$ it also produces the same gas $B.$ $D$ also produces the same gas even on reaction with dilute $H_2SO_4$ at room temperature. Element $A$ imparts a golden yellow color to the Bunsen flame. Then,$A, B, C,$ and $D$ may be identified as:

Which of the following is the correct arrangement in increasing order of solubility?