I think its A but I'm not sure.
The thermodynamic barrier that must be overcome before products are formed in spontaneous reaction is activation energy.
The activation energy is the maximum amount of extra energy that is required by a reacting molecules to get converted into product. It is the minimum energy that is required or needed to activate or energize molecules or atoms.
It is needed in the reaction so that reactants can move together and overcome forces of repulsion and start bond breaking.
Reactant is the substance that takes part in and that undergoes change during a reaction.
To learn more about reactant here
brainly.com/question/17096236
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