Which of the following has the strongest inter-particle force at the room temperature?
The stronger the interparticle forces (between particles), the shorter the distance between those particles.
In solids, stronger interparticle forces exist between the particles, so the particles are much closer than in liquids and gases.
Moreover, chalk and iron both are solids but the intermolecular force of attraction in iron is stronger than that in chalk and this can be understood by hammering chalk and iron. We will observe that the chalk is converted to powder but the iron remains the same.
Since Nitrogen is a gas and Mercury, although a metal, is liquid. Therefore the order of intermolecular force of attraction will be
Nitrogen < Mercury < Chalk < Iron