The electronic configuration of three elements A, B and C are as follows :

A — 2, 8, 8, 2;

B — 2, 8, 7

C — 2, 4

(i) Which of these can form cations ?

(ii) Which of these can form anions ?

(iii) Write a formula of a covalent compound formed using these elements

(i) A will form cations as it will lose electrons to attain a stable octet.

(ii) B will form anions as it will gain electrons to attain a stable octet.

(iii) Formula of a covalent compound formed

$\text{C}^{4} \phantom{\nearrow} \text{B}^{1-} \\[0.5em] \overset{\phantom{3}{4}}{\text{C}} \space {\searrow}\mathllap{\swarrow} \space \overset{1}{\text{B}} \Rightarrow \underset{\phantom{2}{1}}{\text{C}} \space {\searrow}\mathllap{\swarrow} \space \underset{4}{\text{B}} \\[0.5em]$

So, we get the formula as $\bold{CB}_{\bold{4}}$