Chemical reactions can only occur when... 1)particles are able to separate
2) particles mix together
3) particles come together for a sufficient amount of time
4) particles come together with sufficient energy

4). Particles come together with sufficient energy.

Explanation:

According to the collision theory, Molecules must collide with sufficient energy, known as the activation energy, so that chemical bonds can break. Molecules must collide with the proper orientation.

a) the particles of the chair are strongly held together.