A metal M reacts slowly with dry $N X_{2}$ even at room temperature to give a nitride X. X reacts with water to give a gas that turns moist red litmus blue. Which option gives the flame colour of M and the products of strong heating of its nitrate?

Answer: D

Among the s-block metals only lithium forms a nitride with

N X_{2}

at room temperature:

6 Li + N X_{2} 2 Li X_{3} N

, and

Li X_{3} N + 3 H X_{2} O 3 LiOH + NH X_{3}

, the basic gas. Lithium gives a crimson-red flame. Its nitrate follows the pattern of group 2:

4 LiNO X_{3} 2 Li X_{2} O + 4 NO X_{2} + O X_{2}

, unlike the other alkali nitrates which give nitrites.