Answer : At 120°C
Explanation : At 120°C temperature the boiling point of this substance is observed in the given graph.
As per the definition of the boiling point, "It is the temperature at which the vapour pressure of the given substance becomes equal to the standard surrounding atmospheric pressure"
Here, in this graph, it is clearly seen at 120°C where the substance raises to the high temperature and remains stable for certain period of time and then again slightly increases.
