The reaction in which one atom of a molecule is replaced by another atom is called

Options

A. substitution
B. reduction
C. addition
D. double decomposition

Explanation

To solve the question, "The reaction in which one atom of a molecule is replaced by another atom is called," we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify the type of chemical reaction where one atom in a molecule is replaced by another atom.

2. **Review the Options**: We have four options to consider:
- A) Substitution Reaction
- B) Reduction Reaction
- C) Addition Reaction
- D) Double Decomposition Reaction

3. **Define Each Reaction Type**:
- **Substitution Reaction**: This is a reaction where one element replaces another in a compound. For example, if we have a compound AB and a more reactive element C, C can replace A or B to form a new compound.
- **Reduction Reaction**: This involves the gain of electrons or a decrease in oxidation state. It does not specifically involve the replacement of one atom with another.
- **Addition Reaction**: This occurs when two or more reactants combine to form a single product. It does not involve the replacement of atoms.
- **Double Decomposition Reaction**: This involves two compounds reacting to form two new compounds, where components are exchanged. It does not specifically replace one atom with another.

4. **Identify the Correct Reaction**: From the definitions, we can see that the reaction where one atom is replaced by another is specifically described by the **Substitution Reaction**.

5. **Conclusion**: Therefore, the answer to the question is **Substitution Reaction**.

### Final Answer:
The reaction in which one atom of a molecule is replaced by another atom is called **Substitution Reaction**.

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