Assertion :Above critical temperature liquid state cannot be observed. Reason :Above critical temperature, the average kinetic energy of a molecule is always greater than the maximum kinetic energy a molecule can possess in liquid state.

Critical temperature is the temperature at and above which vapor of the substance cannot be liquified, no matter how much pressure is applied. The reason is that average kinetic energy of a gas becomes sufficiently high that it can overcome the intermolecular forces and is greater than the maximum kinetic energy of a molecule can possess in liquid state. Thus, (a) is correct.