What is formed when sodium bicarbonate is heated strongly?

$A$ metal $M$ reacts with $N_2$ to give a compound '$A$' $(M_3N)$. '$A$' on heating at high temperature gives back '$M$' and '$A$' on reacting with $H_2O$ gives a gas '$B$'. '$B$' turns $CuSO_4$ solution blue on passing through it. $A$ and $B$ can be

Which of the following salts does not produce nitrogen dioxide $(NO_2)$ upon heating?

State the reasons for the following:
$(a)$ Why is a solution of $Na_{2}CO_{3}$ alkaline?
$(b)$ Why are alkali metals prepared by the electrolysis of their fused chlorides?
$(c)$ Why is sodium found to be more useful than potassium in biological systems?

Which type of metal is used in a photoelectric cell? Give an example.

Which of the following is the most important biological compound containing $Mg$ found in the living world?