AP EAPCET 23-Aug-2021 Shift 1 Paper

Coordination number of an element depends on the availability of valence shells. Since, carbon is placed in 2 nd period and electronic configuration of C6 is 1s22s22p2. It do not have vacant d-orbital.
Therefore, it has covalency of 4. While germanium is placed in 3rd period in the periodic table.
Electronic configuration of Ge32 is [Ar]3d104s24p2. It has vacant d-orbital.
∴ Germanium can extend its coordination number.