1. According to kinetic theory of ideal gas, molecules of ideal gas should be in incessant random motion and constantly colliding with each other and with the wall of the container in which they are kept.

2. This can only happen when they have large velocities or kinetic energy. And we know that temperature and kinetic energy are directly proportional to each other.

Where K. E=kinetic energy of gas

k_B = Boltzmann constant

T = temperature of gas

So, large kinetic energy means high temperature.

3. Another postulate of kinetic theory states that size of molecule should be very small as compared to the volume of gas.

4. This can be achieved at low pressure because at low pressure concentration of gas is very low (less number of molecule in large volume or space). So, gas behaves as ideal gas at low pressure and at high temperature.