(a(i))[1]
State the observation that supports the assumption that the intermolecular forces in a solid are significant.
(a(ii))[1]
State the observation that supports the assumption that the forces of attraction between molecules in a gas are negligible.
(b)[4]
Explain, on the basis of the kinetic model of gases, the pressure exerted by a gas.
(c)[2]
Liquid nitrogen has a density of $810\ \text{kg m}^{-3}$. The density of nitrogen gas at room temperature and pressure is approximately $1.2\ \text{kg m}^{-3}$. Suggest how these densities are linked to the separation of nitrogen molecules in the liquid and gaseous states.