The bursting of water pipes during very cold weather, when the water in the pipes form ice could be attributed to

Step 1: Analyze the question We are asked why water pipes burst in very cold weather when the water inside turns to ice.

Step 2: The concept Most substances contract when they freeze, but water is unusual. When water cools below 4°C, it begins to expand. When it freezes at 0°C, the molecules arrange into an open hexagonal crystal lattice with more space between them. This makes ice less dense (about 917 kg/m³) than liquid water (1000 kg/m³). It is also why ice floats on water.

Step 3: Solution

• Water fills the pipe.
• The temperature falls below 0°C, and the water freezes.
• The volume increases by about 9% as it turns to ice.
• The pipe walls cannot accommodate this extra volume, so a very large pressure builds up and the pipe cracks or bursts.

Step 4: Check each option

• A. Contraction of pipes when cooled: Pipes do contract slightly, but this effect is tiny and is not the main cause.
• B. Expansion of water on freezing: Correct. This is the direct cause of the pressure that bursts the pipe.
• C. Contraction of water on freezing: Wrong. Water expands when it freezes, it does not contract.
• D. Expansion of ice on melting: Wrong. Ice actually contracts when it melts, and melting is not what bursts the pipe.

**Answer: B. Expansion of water on freezing.

Exam tip: Remember "water is the odd one out": it expands when it freezes. This one fact explains why ice floats, why pipes burst, and why bottles of water crack in a freezer. Whenever you see "freezing" with "bursting" or "cracking", think of expansion.