• Oxidation number also called oxidation state is the number of electrons an atom/molecule accepts or donates in a chemical reaction.
• Whereas, covalency is the shared atoms between two atoms/molecules to attain a stable electronic configuration hence forming covalent bonds.

Sulphur, $S_8$ molecule is also known as octa-Sulphur is a monatomic molecule. Thus its oxidation state is 0 . Each Sulphur atom forms two covalent bonds thus giving a crown-like structure.

Hence, the oxidation number and covalency of Sulphur in $S_8$ molecule are 0 and 2 .