Which of the following statements about the collision theory is correct?

Step 1: Analyze the question We are asked to pick the correct statement about collision theory, which explains how and why chemical reactions occur and how fast they happen.

Step 2: The concept Collision theory says that for a reaction to occur:

1. Reactant particles must collide.
2. They must collide with enough energy, at least the activation energy.
3. They must collide with the proper orientation.

A collision that meets these conditions is an effective collision. Only effective collisions lead to products. The more effective collisions per unit time, the faster the reaction.

Step 3: Check each option

• A. Ineffective collision brings about chemical reaction. Wrong. Ineffective collisions lack sufficient energy or proper orientation, so the particles just bounce off each other.
• B. All collisions bring about reactions. Wrong. Most collisions are ineffective. If all were effective, nearly every reaction would be instantaneous.
• C. The rate of reaction is proportional to the number of effective collisions. Correct. Increasing concentration, temperature, surface area, or adding a catalyst increases the frequency of effective collisions, and so increases the rate.
• D. Collision of molecules will split the molecules to react. Wrong. Collisions do not automatically split molecules. Bonds break only if the colliding particles have enough energy.

Step 4: Answer The correct option is C.

Tip: In collision theory questions, look for the words "effective" or "sufficient energy" and "proper orientation". Statements saying "all collisions" or "ineffective collisions" cause reaction are almost always wrong.