# The stability of +1 oxidation state among Al, Ga, In and Tl increases in the sequence: Option 1) Ga < In < Al < Tl Option 2) Al < Ga < In < Tl Option 3) Tl < In < Ga < Al Option 4) In < Tl < Ga < Al

As we learned in concept no

Inert pair effect -

The phenomenon in which outer shell s electrons (ns2) penetrate to (n-1) d-electrons and thus become closer to nucleus and are more effectively pulled by the nucleus

- wherein

This results in less availability of ns2 electrons pair for bonding or ns2 electron pair becomes inert.

The order of stability of +1 oscidation state is

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This is on account of inert pair effect in which outer shell and electrons $(ns^{2})$ penetrate into (n-1) d electrons and thus become closer to nucleus and are therefore less available for bonding.

Option 1)

Ga < In < Al < Tl

This is incorrect option

Option 2)

Al < Ga < In < Tl

This is correct option

Option 3)

Tl < In < Ga < Al

This is incorrect option

Option 4)

In < Tl < Ga < Al

This is incorrect option

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