UPSC NDA I 2016 General Ability Solved Paper

Concept:Density is mass per unit volume ($\rho = \frac{m}{V}$).Explanation:Water behaves unusually — its density changes with temperature.In ice, molecules are loosely packed with many empty spaces, so density is low.As ice melts, molecules come closer together, reducing volume.At $4^\circ \text{C}$, water molecules are closest packed, giving minimum volume for a given mass.Therefore, density reaches a maximum of $1000\ \text{kg/m}^3$ at $4^\circ \text{C}$.Beyond $4^\circ \text{C}$, volume expands slightly, so density decreases.Answer:Option C: Maximum at $4^\circ \text{C}$.