Activation energy is required for :

Options

A. exothermal reactions
B. endothermal reactions
C. enzyme mediated reactions
D. starting all biochemical reactions

Explanation

**Step-by-Step Solution:**

1. **Understanding Activation Energy**: Activation energy is defined as the minimum amount of energy required to initiate a chemical reaction. It is crucial for all types of reactions, whether they are exothermic or endothermic.

2. **Analyzing the Options**:
- **Option 1: Exothermic Reaction**: Exothermic reactions release energy. While they do require activation energy to start, the focus of the question is on the requirement for activation energy in general, not just for exothermic reactions.
- **Option 2: Endothermic Reaction**: Endothermic reactions absorb energy. Similar to exothermic reactions, they also require activation energy to proceed. However, the question is looking for a broader application.
- **Option 3: Enzyme Mediated Reaction**: Enzyme-mediated reactions involve enzymes that lower the activation energy required for a reaction to occur. While these reactions do require activation energy, the question is asking for a more general context.
- **Option 4: Starting All Biochemical Reactions**: This option correctly identifies that activation energy is required to initiate all biochemical reactions. It emphasizes that activation energy is essential for starting any chemical process.

3. **Conclusion**: Based on the analysis of the options, the correct answer is that activation energy is required for starting all biochemical reactions. Therefore, the right choice is **Option 4**.

**Final Answer**: Activation energy is required for starting all biochemical reactions (Option 4).

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