Mercury is a good choice for thermometers because:

* High Coefficient of Expansion: It expands significantly with temperature changes, making it very sensitive to even small temperature variations.

* Consistent Expansion: Mercury expands at a relatively uniform rate over a wide temperature range, ensuring accurate readings.

* High Boiling Point: It has a high boiling point (357°C), allowing it to be used to measure temperatures up to this point without vaporizing.

* Visible and Easy to Measure: Mercury is a shiny, silver liquid that is easy to see and measure in a thermometer.

However, due to its toxicity and environmental concerns, mercury thermometers are being phased out in favor of safer alternatives like digital thermometers or thermometers using alcohol-based solutions.