A glass of (1) tap water, (2) distilled water and (3) sea water is cooled to its solidification. The order in which they will solidify first is

Answer & Explanation

Correct answer: (D) distilled water, tap water, sea water

• The key principle here is freezing point depression — the presence of dissolved substances (solutes) in water lowers its freezing point below 0°C. The more dissolved substances present, the lower the freezing point.

Analysis of each type of water

Distilled Water — freezes first

• Contains no dissolved substances whatsoever
• Freezing point = exactly 0°C
• Freezes first because it has the highest freezing point

Tap Water — freezes second

• Contains small amounts of dissolved minerals — calcium, magnesium, chlorine, fluoride etc.
• Freezing point = slightly below 0°C (around -0.1°C to -0.5°C)
• Freezes after distilled water due to mild freezing point depression

Sea Water — freezes last

• Contains very high concentration of dissolved salts — primarily sodium chloride (NaCl)
• Average salinity = 3.5% (35 grams of salt per litre)
• Freezing point = approximately -1.8°C to -2°C

Freezes last because it has the lowest freezing point