question_answer 1)

  Assertion (A): Spontaneous process is an irreversible process and may be reversed by some external agency. Reason (R): Decrease in enthalpy is a contributory factor for spontaneity.

Answer:

  (b) Spontaneous processes are irreversible in nature. We know,\[\Delta G=\Delta H-T\Delta S;\,\,\,\Delta G\] must be negative for spontaneous process. Hence decrease in enthalpy will contribute to the condition for spontaneity.