Assertion: In isothermal process, whole of heat energy supplied to the system is converted into internal energy. Reason: According to the first law of thermodynamics U = q - w

For isothermal process, temperature is constant i.e. T=0 Internal Energy, U= nC T v =0 From first law of thermodynamics, U= q+W which suggests that total heat supplied to the system will be converted into work done. Therefore, Both Assertion and Reason are incorrect Hence, correct option is (d)