Question

We are advised to avoid keeping a clinical thermometer in the sun or near a flame. Why?

Answer 1

A clinical thermometer has a small temperature range, i.e. ${35}^{o}Cto{42}^{o}C$. Temperatures under direct sun or near the flame are very high. The glass will crack/ burst due to excessive expansion of mercury inside the capillary tube of a clinical thermometer.
That’s why we should avoid keeping a clinical thermometer in the sun or near a flame.