p-Block Elements-I 1 Question 3
3. The relative stability of +1 oxidation state of group 13 elements follows the order
(2019 Main, 11 Jan II)
(a) $\mathrm{Al}<\mathrm{Ga}<\mathrm{Tl}<$ In
(b) $\mathrm{Al}<\mathrm{Ga}<$ In $<\mathrm{Tl}$
(c) Tl $<$ In $<$ Ga $<$ Al
(d) $\mathrm{Ga}<\mathrm{Al}<$ In $<\mathrm{Tl}$
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Answer:
Correct Answer: 3. (c)
Solution:
- The stability order of +3 and +1 oxidation states of group 13 elements will be:
$$ \begin{gathered} \mathrm{B}^{3+}>\mathrm{Al}^{3+}>\mathrm{Ga}^{3+}>\mathrm{In}^{3+}»\mathrm{Tl}^{3+} \ \quad \text { (order of }+3 \text { oxidation state) } \end{gathered} $$
The presence of two oxidation states in $p$-block elements is due to the inert pair effect.
Because of the presence of poor shielding $d$ and $f$-orbitals, as we move from $\mathrm{Ga}$ to $\mathrm{Tl}$, effective nuclear charge of these elements increases so as to hold the valence $n s^{2}$ electrons tightly. It causes difficulty to the ionisation of $n s^{2}$-electrons and it remains inert, only $n p^{1}$-electron ionises to give +1 oxidation state.
