Answer : +4
Explanation : Carbon's valency is +4.
Valency is defined as the combining or giving away power for required electrons of any element, especially it is measured by the number of hydrogen atoms which can be displaced or combined with.
In carbon which has 6 electrons in its atom. In first shell has 2 electrons and in the second shell 4 electrons are accommodated. It can either donate or accept 4 electrons in its valence shell. Most commonly the valency is +4.
