Question

what may happen if the bulb of thermometer is kept below the surface of water while determining boiling point of water

Answer 1

it may explode if temperature exceed above 100*C

Answer 2

The bulb of thermometer is kept inside the boiling water it may break and the temperature cannot be taken.

That's why, bulb of a thermometer is always kept above the surface of water while determining the boiling point so as to make sure that the bulb doesn't breaks due to very high temperature

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hope it helps.....