Question

Among the following, the element(s) which show inert-pair effect is/are:
A. $Bi$
B. $Sn$
C. $Pb$
D. $C$

Answer 1

Hint:The inert pair effect is the tendency of the two electrons in the outermost atomic s- orbital to remain paired and unshared in some compounds. Those some compounds are post transition metals. It is generally observed in group 13, 14,15.

Complete answer:
According to this inert pair effect as we descend down in the group, the 2 electrons of the S- orbital of valence shell become inert. They do not easily take part in bonding and as a result of this, that element shows its oxidation state two units less than the group oxidation state.
For example: Aluminium has stable oxidation state= +3
Gallium has stable oxidation state= +3
Indium show both oxidation state= +1 and +3
Thallium shows oxidation state= +1
Reason for decrease in oxidation state by 2, on going down the group is the effective nuclear charge increase due to which the penetration effect of s-orbital and d- orbital also increases and hence s-orbital electrons do not take part in bonding. This is known as the inert pair effect of s-electrons. As a result we can say, on going from top to bottom in a group less oxidation state will become more stable.
In nitrogen group, general oxidation state is +5 but bismuth is stable more at +3
In the carbon group, the general oxidation state is +4 but tin can show both oxidation states that are $S{n^{2 + }}$ and $S{n^{4 + }}$. Also lead is more stable at $P{b^{2 + }}$ oxidation state.
All three of them show inert pair effects.

Hence the correct options are A, B, C

Note:
Tin exists as a simple ion tin(II) and is a strong reducing agent. It itself gets oxidized to its another oxidation state that is tin(IV). Tin(IV) generally forms covalent compounds. $Hg$ is difficult to oxidize because it contains only an inert pair of electrons.