What must happen before a chemical reaction can begin?
a) the activation energy must be exceeded.
b) the activation energy must be reached.
c) the concentrations of products and reactants must be equal.
d) the concentration of reactant molecules must be reduced.

I believe the correct response is A. The activation energy must be exceeded.

The metal is named first

Answerδh > 0explanationc₆h₆  (s)  → c₆h₆ (l)if you are changing it from a solid to a liquid, you are pretty much melting the solid. this requires heat energy. therefore, the reaction is endothermic (takes in energy); the system enthalpy increases as the reaction proceeds: δh > 0.