Electromagnets can be created by wrapping a wire around an iron nail and running current through the wire. The electric field in the wire coil creates a magnetic field around the nail. In some cases, the nail will remain magnetised even when removed from within the wire coil
The molecules of different liquids have different size and mass. The mass and size of the molecules in a liquid and how closely they are packed together determine the density of the liquid. Just like a solid, the density of a liquid equals the mass of the liquid divided by its volume; D = m/v. The density of water is 1 gram per cubic centimeter.