Water is readily available but it is not a thermometric liquid mainly because

Analyze the question: We're asked why water, though easily available, is not used as a thermometric liquid. A thermometric liquid must show a regular, uniform change in volume with temperature.

Explain the concept: A good thermometric liquid should:

• Expand uniformly (linearly) with temperature
• Be visible (opaque or colourable)
• Not cling to glass (does not wet it)
• Have a wide liquid range (low freezing point, high boiling point)
• Have a fairly high expansivity and respond quickly to heat

Step-by-step evaluation:

• A. Clings to glass: Water does cling to glass, which is a drawback, but it is not the main reason.
• B. Does not expand uniformly: Water has an anomalous expansion. It contracts when heated from 0°C to 4°C, reaches maximum density at 4°C, and only then expands. Because its volume does not change regularly with temperature, it cannot give a reliable, evenly spaced scale. This is the fundamental reason.
• C. Boils at low temperature: Water boils at 100°C, which is actually fairly high compared with alcohol. So this is incorrect.
• D. Is colourless: Colourless liquids can be dyed (alcohol is coloured red), so this is a minor issue.

Answer: The main reason is that water does not expand uniformly (its anomalous expansion between 0°C and 4°C), which is option B.

Exam tip: Remember "4°C anomaly". Whenever a question asks why water is a poor thermometric liquid, think of its irregular expansion between 0°C and 4°C. Also remember that mercury is preferred because it expands uniformly, is opaque, and does not wet glass.