Can the temperature of an isolated system remain constant?

Assertion: Universe as a whole may be viewed an isolted system. Reason: Total energy of an isolated system remain constant or stretched.

Assertion : If there is no external torque on a body about its centre of mass, then the velocity of the centre of mass remains constant. Reason : The linear momentum of an isolated system remains constant.

Satement-1: if there is no external torque on a body about its centre of mass, then the velocity of the center of mass remains constant. Statement-2: The linear momentum of an isolated system remains constant.

What is an isolated system ?

Equal masses of three non-reacting different ideal gases X,Y and Z are mixed in a sealed rigid container. If the temperature of the system remain constant at 400K, which of the system remain constant at 400K, which of the following statement about gas X can never be correct?

A thermodynamic process in which temperature T of the system remains constant though other variable P and V may change, is called