Explanation:

Valency is the measure of the combining capacity of atoms or molecules. Therefore, it is the capacity of an atom of a single element to react and combine with particular numbers of atoms of another element. The electrons present in the outermost shelVorbit of an atom are called valence electrons. The valence electrons take part in any chemical reaction because the outermost orbit usually contains more energy than the electrons present in other orbits. The valency of an element depends upon the total number of electrons in the outer most shell of an atom.