Question

Why do solids have high densities?

Answer 1

density means mass / volume.
solids has more mass than liquids and gases.
and also has more volume.
so the solids have more density than any other thing..

Answer 2

The solids have high densities because they have strong intermolecular bond.

The density of any object is a physical property that depends on mass and volume.  

Density is the ratio of mass by volume and can be written as:

$\bold{\text{Density} =\frac{\text {Mass}}{\text { Volume }}}$

In solid state, the solid particles are very close to each other due to strong intermolecular force of attraction between them. Therefore, they have least intermolecular space that makes them denser compare to liquids and gases.

Hence, solids have high densities.