What must be true for any endothermic reaction?

a. the chemical bonds of the products have more energy than the chemical bonds of the reactants.
b. there are more products than there are reactants.
c. there must be a phase change from solid to liquid or from liquid to gas.
d. the reaction must take place in a sealed container held at constant volume.

Answer : The correct option is, (a) The chemical bonds of the products have more energy than the chemical bonds of the reactants.

Explanation :

Endothermic reaction : It is defined as the chemical reaction in which the energy is absorbed from the surrounding.

In the endothermic reaction, the energy of reactant are less than the energy of product.

Exothermic reaction : It is defined as the chemical reaction in which the energy is released into the surrounding.

In the exothermic reaction, the energy of reactant are more than the energy of product.

Hence, the correct option is, (a) The chemical bonds of the products have more energy than the chemical bonds of the reactants.

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.