Why is dioxygen a gas but sulphur a solid ?

Explanation

Oxygen because of its small size and high electronegativity forms pn-pn multiple bonds.
This tendency is absent in sulphur due to its large size. Also, the bond enthalpy of (O = O) is quite large as compared to (S = S) while bond enthalpy of (S - S) is larger as compared to (O-O). Thus -S-S-S- chains are more stable than -O-O-O-chains. So, `O_2` is gas and `S_8` is a solid.