The reaction between ethylene and hydrogen in thepresence of hot nickel powder is called

Options

A. substitution reaction
B. dissociation reaction
C. addition reaction
D. decomposition reaction

Explanation

To solve the question regarding the reaction between ethylene and hydrogen in the presence of hot nickel powder, we will analyze the types of chemical reactions and identify the correct classification for this particular reaction.

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are ethylene (C2H4) and hydrogen (H2). Ethylene is an alkene, which contains a carbon-carbon double bond.

2. **Understand the Role of Nickel**: Nickel acts as a catalyst in this reaction. A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. In this case, hot nickel facilitates the reaction between ethylene and hydrogen.

3. **Determine the Type of Reaction**:
- **Substitution Reaction**: This involves one atom or group being replaced by another atom or group. This does not apply here since we are not replacing any atoms.
- **Dissociation Reaction**: This involves breaking down molecules into simpler molecules, atoms, or radicals. This does not apply as we are not breaking down the reactants.
- **Addition Reaction**: This involves combining two or more reactants to form a larger molecule. In this case, hydrogen is adding across the double bond of ethylene, converting it into ethane (C2H6).
- **Decomposition Reaction**: This involves breaking down a compound into simpler substances. This does not apply here as we are not breaking down any compounds.

4. **Conclusion**: Since hydrogen is adding to ethylene to form ethane, the reaction is classified as an **addition reaction**.

5. **Final Answer**: The reaction between ethylene and hydrogen in the presence of hot nickel powder is called an **addition reaction** (Option C).