Arrange the following as per the instruction given in the bracket.
$\mathrm{N}\mathrm{a}, \mathrm{L}\mathrm{i}, \mathrm{K}$(Increasing ionisation energy).

Match the atomic number $2,4,8,15$ and $19$ with each of the following:

(i) A solid non-metal belonging to the third period.

(ii) A metal of valency $1$.

(iii) A gaseous element with valency $2$.

(iv) An element belonging to group $2$.

(v) A rare gas.

Rewrite the following sentence by using the correct symbol $>$ (greater than) or $<$ (less than) in the blank given.

The ionisation potential of potassium is less than _____ that of sodium.