At high pressure and high temperature
At low pressure and high temperature
At low pressure and low temperature
At high pressure and low temperature
At high pressure and low temperature, a gas deviates the most from its ideal behaviour. Under these conditions, the gas molecules are close to each other and they exert significant intermolecular forces on each other. Also, the volume of gas molecules becomes a significant portion of the total volume and cannot be neglected. Hence, the correct option is D.