The element A burns in nitrogen to give an ionic compound B. The...

\text{A}\overset{\text{burns,}\text{nitrogen}}{→} \mathop{B}_{\text{ionic}\text{compound}} \overset{{H}_{2} \text{O}}{→} \mathop{C}_{\text{milky}\text{solution}} \text{+}\text{D}\overset{{\text{CO}_{2}}{→}$<br />Since the solution of C becomes milky on bubbling$C{O}_{2}$into it, C is lime water$( Ca\left(OH{)}_{2}\right).$Thus, the element A is calcium and B is the compound of calcium with nitrogen. Nitrides on reacting with water give the corresponding hydroxide and ammonia. Therefore,<br />A is calcium (Ca)<br />B is calcium nitride$\left(C{a}_{3}{N}_{2}\right)$.<br />C is lime water$Ca{ \left(OH\right)_{{2}}<br />D is ammonia \left(N{H}_{3}\right).
$\text{Ca}$\overset{\text{burns,}\text{nitrogen}}{→} \mathop{{$\text{Ca}_{3}$ {N}_{2}}_${\text{ionic}\text{compound}}$ \overset{{H}_{2} $\text{O}$}{→} \mathop{$\text{Ca}${( $\text{OH}$ )}_{2}}_${\text{milky}\text{solution}}$ + {$\text{NH}_{3}$ \overset{{\text{CO}_{2}}{→} {$\text{CaCO}_{3}$