Question

the valency of carbon is 4 why

Answer 1

A carbon atom has four electrons in its outermost valence shell. So, it needs four more electrons to complete its octet. A carbon atom completes its octet only by sharing its valence electrons with other atoms. As a result, a carbon atom forms four covalent bonds by sharingvalence electrons with other atoms.

Answer 2

because atomic number of Carbon is 6.
electronic configuration is : 1s2,2s2 2p2
now to complete 8 electrons in the outer shell it need 4 electrons.
so,its valency is 4