Discuss the pattern of variation in the oxidation states of (a)`B to TI` and (b) `C to Pb`.

Explanation

(i) B to TI
The electric configuration of group 13 elements is `ns^(2)" "np^(1)`. Therefore, the most common oxidation state exhibited by them should be +3. However, it is only boron and aluminium which practically show the +3 oxidation state. The remaining elements, i.e., Ga, In, Tl, show both the +1 and +3 oxidation states. On moving down the group, the +1 state bocmes more stable. For example, Tl (+1) is more stable than Tl(+3). This is because of the inert pair effect. The two electrons present in the s-shell are strongly attracted by the nucleus and do not participate in bonding. This inert effect becomes more and more prominent on moving down the group. Hence, Ga (+1) is unstable, In (+1) is fairly stable, and Tl (+1) is very stable.
`{:("Group 13 element","Oxidation state"),(B,+3),(Al,+3),("Ga,In,Tl","+1,+3"):}`
The stability of the +3 oxidation state decreases on moving down the group.
(ii) C to Pb
The electronic configuration of group 14 elements is `ns^(2)" "np^(2)`. Therefore, the most common oxidation state exhibited by them should be +4. However, the +2 oxidation state becomes more and more common on moving down the group. C and Si mostly show the +4 state. On moving down the group, the higher oxidation state becomes less stable. This is because of the inert pair effect. Thus, although Ge, Sn, and Pb show both the +2 and +4 states, the stability of the lower oxidation state increases and that of the higher oxidation state decreases on moving down the group.
`{:("Group 14 element","Oxidation state"),(C,+4),(Si,+4),("Ge,Sn,Pb","+2,+4"):}`
`overset("stability of +2 state increases")rarr`
`underset("stability of +4 state decreases")overset("C "Si" "Ge" "Sn" "Pb")rarr`