JEE Main 2025 · 29 January · evening · Single correct · +4 / −1
Given below are two statements :
Statement (I): NaCl is added to the ice at 0°C, present in the ice cream box to prevent the melting of ice cream.
Statement (II): On addition of NaCl to ice at 0°C, there is a depression in freezing point.
In the light of the above statements, choose the correct answer from the options given below :
- (a) Both Statement I and Statement II are false
- (b) Statement I is true but Statement II is false
- (c) Both Statement I and Statement II are true
- (d) Statement I is false but Statement II is true
Answer and solution
Answer (c) Both Statement I and Statement II are true
Solution
Chemistry ma’am · 4 steps
Salt makes the ice colder, not warmer: brine freezes below 0°C, so the ice cream stays frozen.
- Statement II. NaCl dissolves in the thin film of water on the ice and forms brine. A solution freezes at a lower temperature than pure water, so the freezing point drops below 0 °C. Statement II is true.
Δ T_f = i K_f m, i ≈ 2 for NaCl
- What the ice does. At 0 °C the ice is now above the brine's freezing point, so some ice melts. Melting absorbs latent heat from the surroundings, and the ice-salt mixture cools to well below 0 °C.
- Statement I. This colder mixture keeps the ice cream from melting. That is why salt is added to the ice in the box, so Statement I is true, and Statement II is the reason it works.
- So. Both statements are true, which is option (c).
The idea to keep. Adding a solute lowers the freezing point. Ice at 0°C then melts, absorbs heat, and the mixture cools below 0°C. Salt on ice is a cooling trick.
Answer from the NTA final answer key. Solution by PrepWiser.