Question

Oxygen is a gas but sulphur is a solid

Answer 1

Oxygen is smaller in size as compared to sulphur. Due to its smaller size, it can effectively form p-pi p-pi bonds and forms diatomic O2 (O==O) molecule. The intermolecular forces in oxygen are weak van der Waals forces, which causes it to exist as gas. On the other hand, sulphur does not form strong S=S double bonds hence exists as a puckered structure held together by strong covalent bonds and exists as a polyatomic molecule. So, it exists as a solid.