Water is not a good thermometric liquid because it?

Analyze the question: A thermometric liquid must change volume regularly (uniformly) as temperature changes, so that the scale on the thermometer is evenly spaced. We need the reason water fails this requirement.

Explain the concept: Most liquids expand steadily when heated. Water is unusual. When you heat it from 0 °C to 4 °C, it contracts instead of expanding, so its density increases and reaches a maximum at 4 °C. Above 4 °C, it begins to expand normally. This is called the anomalous expansion of water.

Because of this, the same thermometer reading could correspond to two different temperatures (for example, the volume of water at 2 °C is the same as at about 6 °C). It also means water does not expand uniformly with temperature.

Check each option:

• A. expands unevenly between 0 °C and 4 °C: This matches the anomalous expansion. It is the correct reason.
• B. maintains fixed density: False. Water's density changes with temperature, and that is the problem.
• C. has low freezing point: False. Water freezes at 0 °C, which is actually relatively high compared with thermometric liquids like alcohol (about -114 °C) or mercury (-39 °C). So a high freezing point is a limitation, not a low one.
• D. wets glass: Water does wet glass, which is a drawback too (mercury doesn't wet glass), but it is not the main reason for rejecting water. Also, water is colourless and a poor conductor of heat, which adds to its unsuitability.

Answer: The best option is A, since anomalous expansion between 0 °C and 4 °C is the classic textbook reason.

Tip: Remember "Water is weird from 0 to 4": it contracts when heated in that range, with maximum density at 4 °C. Whenever you see "thermometric liquid" and water, think of anomalous expansion.