Elements of group 14
(a) exhibit oxidation state of +4 only
(b) exhibit oxidation state of +2 and +4
(c) form `M^(2–)" and "M^(4+)` ions
(d) form `M^(2+)" and "M^(4+)` ions

Explanation

Due to inert pair effect, element of group 14 exhibit oxidation states of `+2` and `+4`. Thus option (b) is correct.