Answer;
B. Collision theory
Step-by-step explanation;
The collision theory explains that gas-phase chemical reactions occur when molecules collide with sufficient kinetic energy.
The collision theory is based on the assumption that for a reaction to occur it is necessary for the reacting species (atoms or molecules) to come together or collide with one another.
According to collision theory Molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break.