Question

A real gas behaves most nearly like an ideal gas

Answer 1

Answer: at low pressure and high temperature.

The real gases deviate from ideal gases at high pressures and low temperatures, because high pressure and low temperatures reduce the free space between the particles and their velocities, causing that the effect of the volume of the particles of the gas and the intermolecular forces be more important.

The lower the pressure and the higher the temperatures the less the effect of the volume of the particles and of the intermolecular forces. Remember that ideal gas theory considers that individual particles do not occupy space and they do not intereact one to each other (except for the collisions).