In order for a collision to be effective, which of the following statements are true?

a) The collision geometry of the reactants must be favourable
b) The collision must occur with sufficient energy
c) The collision must occur at the correct time
d) Both a and b are correct
e) All three statements are correct

All three statements (a, b, and c) are correct. For a collision to be effective, the collision geometry of the reactants must be favorable, meaning that the reactant molecules must collide in a way that allows for the necessary chemical bonds to break and new bonds to form. Additionally, the collision must occur with sufficient energy to overcome the activation energy barrier for the reaction to occur. Finally, the collision must occur at the correct time, which is often determined by factors such as temperature and concentration.