The normal boiling point of a liquid is defined as

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