Sodium oxide $(Na_2O)$ is produced when

Which of the following compounds is used as a fire extinguisher?

The colour given to the flame by sodium salts is

$A$ metal on combustion in excess air forms $X$. $X$ upon hydrolysis with water yields $H_2O_2$ and $O_2$ along with another product. The metal is

Arrange the following compounds in the increasing order of their thermal stability. Identify the correct sequence.
$I - K_2CO_3, II - MgCO_3, III - CaCO_3, IV - BeCO_3$

$A$ metal $M$ reacts with nitrogen gas to afford $M_3N$. $M_3N$ on heating at high temperature gives back $M$ and on reaction with water produces a gas $B$. Gas $B$ reacts with aqueous solution of $CuSO_4$ to form a deep blue compound. $M$ and $B$ respectively are