Option d. i<u><em>t is higher than the energy of both reactants and products</em></u>
Explanation:
<em>Activated complex</em>, also known as transition state, is the intermediate structure formed in the course of a chemical reaction.
The activated complex is very unstable and of short life: it is at the peak of the potential chemical diagram, and can transform either into the reactants (backward) or the products (forward).
The activation energy of the reaction is the energy needed to reach the activated complex, then both reactants and products are lower in potential chemical energy than the activated complex, which is what explains why the activated complex can transform into one or another, reactants or products.
A coffee cup calorimeter is great for measuring heat flow in a solution, but it can't be used for reactions that involve gases since they would escape from the cup. The coffee cup calorimeter can't be used for high-temperature reactions, either, because they would melt the cup.
