why or how potential energy is developed due to intermolecular force in an ideal gas and why it is negative?
Most actual all the gases behave approximately as ideal gases, except at very low temperatures because at low temperature the potential energy of their intermolecular forces is high relative to the kinetic energy of the molecules and becomes significant. Under very high pressures when the molecules are packed so close together that close-range intermolecular forces become significant.
Potential energy is negative when the forces are attractive in nature.