Question

Why oxide n is a gas but sulphur is solid?

Answer 1

• Oxygen exist as a diatomic molecule $\left(O_2\right)$ as it forms one $p\sigma -p\sigma$ bond by axial overlap of two p-orbitals & one $p\pi -p\pi$ bond by lateral overlap of two p-orbitals due to its small atomic size.
  
• So due to this, the Van der Waals Forces acting on the $O_2$ is very less. So oxygen exist in gaseous state at room temperature.
  
• On the other hand, sulphur doesn't exist as diatomic molecule as it can only form $p\sigma -p\sigma$ bond & not $p\pi -p\pi$ as lateral overlap is not possible because of large atomic size of sulphur atom. So instead, sulphur exist as octatomic molecule $(S_8$). Now since sulphur molecule is made up of 8 sulphur atoms, the Van der Waals Forces acting on $S_8$ is comparitively higher. So $S_8$ molecules are much closely packed compared to $O_2$molecules.
  
• So, Oxygen exist as gas whereas sulphur exist as solid.