JEE Main 2025 Apr 3 Shift 1, Physics Q1: Change of State And Calorimetry

When ice melts to water at $0^{\circ }$C, its volume decreases (ice is less dense than water). Since the surroundings are at atmospheric pressure, the atmosphere pushes the system inward as the system contracts, so the atmosphere does positive work on the ice-water system.

Equivalently, the work done by the system $W_{\text{by}}=p\Delta V<0$, so the work done on the system is positive.

Heat is absorbed during melting ($Q>0$), and by the first law $\Delta U=Q+W_{\text{on}}$ both terms contribute positively, so internal energy actually increases. Only statement (4) is correct.