Oxgen is a gas, but other element of group 16 th are solids at room temperature. Why?

Explanation

Oxygen exist as isolated diatomic molecules. Between atoms of oxygen molecule the attractions are strong, but inter molecular attraction are very week. Hans oxygen is a gas.
Other elements of of group 16, have complex States. The tendency to forms multiple bonds between identical atoms decrease with an increase in atomic weight, bonding ability between many atoms of of same element increases. Molecular complexity and van der Waals Force increases. Hence, they are solilds.