Question

Aluminum exhibits +3 oxidation states. As we move down the group, +1 oxidation state gets more stable. This is a consequence of:
(A) Increasing size of the atom
(B) inert pair effect
(C) electron-deficient nature
(D) $p\pi -p\pi $ Bonding

Answer 1

Hint: The increasing preference for an oxidation state two lower than maximum valence is not restricted to the group 13 elements. It is a common feature of the post-transition element that these elements act as near inert gas configuration. Group 14 and group 15 also observed this common feature.

Complete step by step solution:
The oxidation of elements in groups does not impact by increasing the size of the atom in group 13 elements. Metals and metalloids of p-block possess common two stable oxidation states to ns and np electrons and also lose two fewer electrons. This is observed mainly in groups 13, 14, and 15 metals.
In group 13, the +3 oxidation state order of preference is, $A{{l}^{+3}}>G{{a}^{+3}}>I{{n}^{+3}}>T{{l}^{+3}}$
The lower oxidation order of preference is, $A{{l}^{+}}The reason for this abnormal behavior is that the heavier elements $n{{s}^{2}}$ valence electrons are chemically inert, i.e, inert pairs. For this reason, there is an increasing preference for the lower oxidation state on moving down the group that has been named as the inert pair effect.
The inert pair effect is defined as “the non-participation of the two s electrons in bonding due to the high energy needed for pairing them”.
Hence, Aluminum exhibits +3 oxidation states. As we move down the group, the +1 oxidation state gets more stable. This is a consequence of the inert pair effect.

The correct answer is option B.


Note: Due to this inert pair effect in group 13, the most stable oxide of Al is aluminum oxide $A{{l}_{2}}{{O}_{3}}$ and the most stable oxide of Thallium is thallium oxide $Tl{{O}_{2}}$ . The inert pair effect is due to the decrease in bond energies down a group.