Question

why is the valency of carbon 4 but not 2

Answer 1

because valence electrons are 4 it could either lose or gain 4 electrons but both gaining or losing is not possible

Answer 2

because the total valence electron (I, e outermost orbit electron )no is 4. And the valency of carbon may be c4- or may be c4+ that is it may gain 4 e-or may loss 4e-.And it is not possible to make valencies of C because in doing so it requires a large amount of energy