Question

Which of the following element shows only $+3$ oxidation state?

• A. $B$
• B. $Al$
• C. $Ga$
• D. $In$

Answer 1

The correct option is A $B$

Option $\left(A\right)$ is correct.

Boron shows only $+3$ oxidation state.

Electronic configuration of boron family is $n{s}^{2}n{p}^1$. The atoms of these elements have 3 valence electrons, therefore all these elements show maximum of + 3 oxidation state. Boron shows only +3 oxidation state in its compound & other elements also show +1 oxidation state.The stability of the +3 oxidation state decreases on moving down the group.

The +1 oxidation state becomes more stable as we move down to the group from boron to thallium because of inert pair effect.In the case of the last element, after the removal of one electron from $p$ orbital, the remaining $n{s}^2$ are strongly attracted by the nucleus and do not participate in bonding.