Question

Even though the atomic number of Carbon is 6, why is it's valency 4?

Answer 1

because carbon required only four e to become stable

Answer 2

in electronic cofiguaration carbon is 1s2 2s2 2p2  1s orbital is ful filled we will not consider it but p is not fulfilled after hybridization 2s orbital denote 1 electron to p orbital then s and p are half filled electron as they are stable so, carbon valency we will take as 4