$(a)$ 'Sodium is a highly reactive metal and it cannot be obtained from its oxide by heating with carbon'. Give reason.
$(b)$ How can sodium be obtained from sodium chloride?

Which gas can be adsorbed on a metal and released when required?

What is the number of electrons lost by a metal atom to form a positive ion called?

$(a)$ Why does calcium start floating when added to water?
$(b)$ Most metals do not release hydrogen gas when reacting with nitric acid. Why?
$(c)$ Write the chemical equation for the reaction of iron with steam. Name the compound of iron obtained.

A non-metal $A$, which is the largest constituent of air, when heated with $H_2$ in a $1 : 3$ ratio in the presence of a catalyst $(Fe)$, gives a gas $B$. On heating with $O_2$, it gives an oxide $C$. If this oxide is passed into water in the presence of air, it gives an acid $D$, which acts as a strong oxidising agent.
$(a)$ Identify $A$, $B$, $C$, and $D$.
$(b)$ To which group of the periodic table does this non-metal belong?

What is the color of copper carbonate salt?