Question

why oxygen is gas and sulphur is solis

Answer 1

Oxygen is smaller in size as compared to sulphur. Due to its smaller size it can easily form pπ– pπ bond and exist as O=O . Also intermolecular forces in oxygen are weak van der Walls which cause it to exist as gas. Whereas sulphur can't form  pπ– pπ  bonds and has puckered ring structure held together by covalent bonds .So it is solid.

Answer 2

Oxygen is smaller in size as compared to sulfur.As oxygen is smaller it can form pπ-pπ bond and the intermolecular forces in Oxygen are weak.So it is a gas.And sulfur doesn't form pπ-pπ bond.It is held together by strong covalent bond and it exists as a polyatomic molecule.So the intermolecular forces are strong.That's why sulfur is solid.

Hope it helps.