An unknown, clear liquid is given to you in a beaker. you transfer the liquid from the beaker to a clean, empty test-tube, and begin to heat it. after a while, you see vapours (which on further analysis you discover are vapours of water) rising from the test-tube, and pretty soon, all that's left are a few crystals of salt stuck to the edges!

was that liquid an element, compound or a mixture?

intermolecular forces are the forces between molecules or particles.

there are two kinds of van der waals forces: weak london dispersion forces and stronger dipole-dipole forces.

in molecule of water there are dipole-dipole forces between negatively charged oxygen from one molecule of water and positively charger hydrogen of another molecule of water.

hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (h), covalently bound to a highly electronegative atom such as flourine (f), oxygen (o) and nitrogen (n) atoms.