Option (2): From the First Law (dQ = dU + dW dW = -dU$dQ = dU + dW \implies dW = -dU$), the work done equals the decrease in internal energy.
Option (4): The internal energy of an ideal gas (dU = n Cv dT$dU = n C_{\mathrm{v}} dT$) increases directly as temperature increases.
Step 2: Final Conclusion
The statement 'The molar heat capacity is zero' is true.
Pattern Recognition
Adiabatic = no heat flow (dQ=0$dQ=0$). Since molar heat capacity tracks the ratio of heat input to temperature change, C$C$ must be 0. Conversely, isothermal has infinite capacity because heat is absorbed without any temperature change (dT=0$dT=0$).
Practice past-year questions one chapter at a time. Pick an exam → subject → chapter and get every PYQ for that topic — pulled together from all past papers — with the chapter's key formulas alongside.
