What is necessary for reactants to combine chemically?

release of energy

input of energy

must satisfy a reversible reaction

equilibrium

Answer: Input of energy

Explanation:

The necessary reactant for a chemical reaction to take place is the input of energy. The reactants combine together in order to get the desired product.

This reaction cannot be carry forward without the supply of energy. This is because energy is required to start a reaction. This energy is known as the activation energy.

so, in order for any reaction to proceed there must be a proper input of energy.

Input of energy is the correct answer