According to Arrhenius theory, the activation energy is

Options

A. The energy it should possess so that it can enter into an effective collision
B. The energy which the molecule should possess in order to undergo reaction
C. The energy it has to acquire further so that it can enter into a effective collision
D. The energy gained by the molecules on colliding with another molecule

Explanation

**Step-by-Step Solution:**

1. **Understanding Activation Energy:**
- According to Arrhenius theory, activation energy (Ea) is defined as the minimum amount of energy that reacting molecules must possess in order to undergo a chemical reaction. This energy is necessary for the reactants to overcome the energy barrier and form products.

2. **Evaluating the Statements:**
- We need to analyze the given statements regarding activation energy:
- **Statement 1:** "The energy it should possess so that it can enter into effective collision."
- This statement is incorrect because activation energy refers to the energy required to initiate a reaction, not just to enter into a collision.

- **Statement 2:** "The energy which the molecule should possess in order to undergo reaction."
- This statement is partially correct, as it implies that the molecules need a certain amount of energy to react, but it lacks the context of "minimum energy" and "effective collision."

- **Statement 3:** "The energy it has to acquire further so that it can enter into effective collision."
- This statement is correct. It indicates that the molecules need to acquire additional energy to reach the threshold for effective collisions that lead to a reaction.

- **Statement 4:** "The energy gained by the molecules on colliding with another molecule."
- This statement is incorrect because molecules do not gain the required activation energy from collisions; rather, they must have sufficient energy before the collision to react.

3. **Conclusion:**
- Based on the analysis, the correct definition of activation energy according to Arrhenius theory is best captured by Statement 3: "The energy it has to acquire further so that it can enter into effective collision."