The forces of attraction between single atoms is very weak so the noble gases all have low melting and boiling points. Melting and boiling points increase going down the group, as the atoms get larger.
The group 0 elements are in the gas state at room temperature and pressure. This is because their boiling points are below room temperature.
Radon is situated below xenon in group 0. Predict the likely boiling point of radon.
The actual boiling point of radon is -61.7°C. An estimate would lie mid-way between -100°C and -50°C based on the shape of the graph.
The particles in gases are widely spaced, so the noble gases have low densities. The density increases going down the group because the atoms have greater mass but the gas takes up the same volume.