To help the chemist get the two substances to react, he can consider the following options:
b. crush up one of the substances - Crushing a solid substance increases its surface area, allowing for more interactions between the reactant particles, which can facilitate a reaction.
c. increase the concentration of one of the substances - Increasing the concentration of one of the reactants increases the number of reactant particles in a given volume, leading to a higher likelihood of collisions and reactions.
d. heat the substances - Heating the substances typically provides the reactant molecules with more kinetic energy, which can increase the frequency and energy of collisions between them, improving the chances of a reaction.
Therefore, the best options to possibly get the substances to react are b, c, and d.
Options a (decreasing the concentration) and e (cooling the substances) are less likely to facilitate a reaction, as they would reduce the number of collisions between reactant molecules.