Which of the following metals displaces $SO_2$ gas from concentrated sulphuric acid?

Zinc $(II)$ ion on reaction with $NaOH$ first gives a white precipitate which dissolves in excess of $NaOH$ due to the formation of:

What is the order of ionic conductivity for the given cations at a specific concentration?

Assertion $A$: Alkali metal elements impart characteristic colors to the flame in a flame test.
Reason $R$: They have very low ionization enthalpy.

Which of the following elements does not occur in liquid form at room temperature?

Calcium on heating in $N_2$ yields an ionic compound $A$, which reacts with water to give $Ca(OH)_2$ and a gas $B$. Identify $A$ and $B$.