JEE Main · 2019 · 09 Jan 2019 · Shift 1 · p-Block Elements

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Aluminium is usually found in +3 oxidation state. In contrast, thallium exists in +1 and +3 oxidation states. This is due to

(A)inert pair effect✓ Correct
(B)diagonal relationship
(C)lattice effect
(D)lanthanoid contraction

Answer: (A)

Solution

Thallium sits at the bottom of group 13 with its configuration ending in

6 s^{2} 6 p^{1}

. The

6 s^{2}

pair is held tightly and shielded poorly by the intervening

4 f

and

5 d

electrons, so it resists taking part in bonding. That reluctance, the inert pair effect, lets thallium show the

+ 1

state alongside

+ 3

, while the lighter aluminium shows only

+ 3

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Single correct option

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