p-Block Elements-I - Result Question 32
####3. The relative stability of +1 oxidation state of group 13 elements follows the order
(2019 Main, 11 Jan II)
(a) $Al<Ga<Tl<$ In
(b) $Al<Ga<$ In $<Tl$
(c) Tl $<$ In $<$ Ga $<$ Al
(d) $Ga<Al<$ In $<Tl$
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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:
$$ \begin{gathered} B^{3+}>Al^{3+}>Ga^{3+}>In^{3+}»Tl^{3+} \ \quad \text { (order of }+3 \text { oxidation state) } \end{gathered} $$
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 $Ga$ to $Tl$, 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.
