The catalytic activity of transition metals and their compounds is mainly due to

Options

A. their magnetic behaviour
B. their unfilled d-orbitals
C. their ability to adopt variable oxidation state
D. their chemical reactivity

Explanation

**Step-by-Step Solution:**

1. **Understanding Transition Metals**: Transition metals are elements found in the d-block of the periodic table. They have unique properties that make them useful as catalysts.

2. **Catalytic Activity**: The catalytic activity of transition metals and their compounds is influenced by several factors. These include their ability to form unstable intermediates, their magnetic behavior, their chemical reactivity, and their unfilled d-orbitals.

3. **Variable Oxidation States**: One of the key characteristics of transition metals is their ability to exhibit variable oxidation states. This means they can lose different numbers of electrons, allowing them to participate in various chemical reactions.

4. **Formation of Unstable Intermediates**: When transition metals act as catalysts, they often form unstable intermediates during the reaction process. This is crucial because these intermediates can lower the activation energy required for the reaction to proceed.

5. **Effect on Activation Energy**: By lowering the activation energy, transition metals increase the rate of the reaction. This is because the activation energy is the minimum energy required for reactants to convert into products.

6. **Conclusion**: Therefore, the catalytic activity of transition metals and their compounds is mainly due to their ability to adopt variable oxidation states, which allows them to form unstable intermediates and reduce activation energy.

**Final Answer**: The catalytic activity of transition metals and their compounds is mainly due to their ability to adopt variable oxidation states.

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