Write is quantum mechanical liquid i.e. helium (II) ? Give its two important characteristics.

Answer

If Helium is compressed and liquefied it forms `He(I)` liquid at 4.2 K.This liquid is a normal liquid like any other liquid.But if it is further cooled then He(II) is obtained at 2.2 K, which is known as super fluid, because it is a liquid with properties of gases.It climbs through the walls of the container & comes out. It has very high thermal conductivity & very low viscosity.