Which kind of impurities are present in the ores? What are these impurities collectively known as?

Which of the following represents the correct order of reactivity of metals?

Write true or false for the following statement:
Hydrogen gas is evolved when a metal reacts with nitric acid.

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 chemical formula of oleum?

Which one of the following metals does not react with cold as well as hot water?