Question

what is the difference between valency and oxidation number.

Answer 1

Valency is the capacity of combining of an atom

Answer 2

1. Valency is the maximum number of electrons which an atom can lose or gain while oxidation state is the actual number of electrons which the element lose or gain to form a molecule.
2. Valency is the property of an isolated atom while oxidation state is calculated for an atom present in a molecule i.e. in bonded state.
3. Oxidation state may or may not be equal to the valency.
4. Valency of an element always remains the same, while its oxidation state may be different in different molecules.