JAMB Chemistry 2019 Paper

Concept:The rate of gas evolution increases when reactants collide more often or more effectively.Explanation:Increasing the concentration of $HCl$ raises the number of acid particles available.More collisions with $CaCO_3$ occur per second, so $CO_2$ is produced faster.Increasing the surface area of solid $CaCO_3$ exposes more particles to the acid.This also increases the collision frequency and speeds up the reaction.Therefore, both factors listed in A and B will increase the rate of $CO_2$ evolution.Answer:C. A and B