AIIMS 2018 Chemistry First Law of Thermodynamics Assertion Reason Question

Option B is correct because both the assertion and the reason are true: in free expansion, the internal energy change (ΔU) is zero, and the work done (W) is also zero, as no external pressure is applied. However, the reason does not explain the assertion directly; the zero work done does not lead to the zero change in internal energy, as they are independent outcomes of the process. Option A is incorrect because the reason does not provide a correct explanation for the assertion. Options C and D are incorrect since both the assertion and reason are indeed true statements about free expansion in thermodynamics.