Which of the following actions will increase the frequency of collisions in a chemical reaction?

Let's analyze each option, Yano, to see which one increases the frequency of collisions:

• A. Lower the temperature of the reaction mixture. Lowering the temperature reduces the kinetic energy of the reactant particles, causing them to move slower. Slower movement leads to fewer collisions per unit time.
• B. If a solid is reacting with a solution, break the solid into smaller pieces. Breaking a solid into smaller pieces increases its total surface area. A larger surface area exposes more reactant particles to the other reactants, leading to a higher frequency of collisions.
• C. For reactions involving solutions, decrease the concentration of the solution. Decreasing the concentration means there are fewer reactant particles in a given volume. With fewer particles, the chances of them colliding decrease, thus lowering the frequency of collisions.
• D. For reactions involving gaseous reactants, decrease the pressure of the gases. Decreasing the pressure of gases means the gas particles are spread out over a larger volume. This reduces the number of particles per unit volume, leading to a lower frequency of collisions.

Therefore, increasing the surface area of a solid reactant by breaking it into smaller pieces will increase the frequency of collisions.

The correct option is $\boxed{\text{B}}$.