JAMB Chemistry 1978 Question 30

The normal boiling point of a liquid is defined as

1. A.the temperature at which its vapour pressure equals the atmospheric pressure
2. B.the temperature at which bubbles begin to form
3. C.the temperature at which the vapour pressure equals 1 temperature
4. D.the temperature at which the rate of condensation of vapour equals the rate of vaporisation of the liquid
5. E.the temperature at which the space above the liquid is saturated.