4.
The diagram shows the energy profile of a chemical reaction. Two energy changes are labelled \( X \) and \( Y \).
Which statement about the reaction is correct?
A The activation energy of the reaction is \( X+Y \).
(B) The enthalpy change of the reaction is \( X \).
C The enthalpy change of the reaction is \( X+Y \).
D The reaction is exothermic.
5.