Activation energy-

Options

A. Is the difference in the average energy content of 'S' from that of its transition state
B. Helps to change reactants into unstable transition state before they can be converted into products
C. Is the minimum energy required from outside to overcome the energy barrier of reactant or to start a reaction
D. All are correct

Answer

**Step-by-Step Solution:**

1. **Understanding Activation Energy**: Activation energy (Ea) is defined as the minimum amount of energy required to initiate a chemical reaction. It is the energy barrier that reactants must overcome for the reaction to proceed.

2. **Analyzing the Options**:
- **Option 1**: "The differences in the average energy content of substrate from that of its transition state." - This describes the energy difference but does not define activation energy.
- **Option 2**: "Help to change reactant into an unstable transition state before they can be converted into products." - This describes the process but does not define activation energy.
- **Option 3**: "The minimum energy required from outside to overcome the energy barrier of reactant or to start a reaction." - This accurately describes activation energy.
- **Option 4**: "The maximum energy required from outside to overcome the energy barrier of reactant or to start a reaction." - This is incorrect as activation energy is a minimum, not maximum.
- **Option 5**: This option is a repetition of Option 4 and is also incorrect.

3. **Conclusion**: The correct definition of activation energy is found in **Option 3**: "The minimum energy required from outside to overcome the energy barrier of reactant or to start a reaction."

**Final Answer**: Activation energy is the minimum energy required from outside to overcome the energy barrier of reactant or to start a reaction (Option 3).

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