A barn is a unit in nuclear chemistry. One barn is
a. `10^(-24) cm^(2)` b. `10^(-3) cm^(2)` c. `10^(-26) cm^(2)` d. `10^(-6) cm^(2)`

Options

A. a. `10^(-24) cm^(2)`
B. b. `10^(-3) cm^(2)`
C. c. `10^(-26) cm^(2)`
D. d. `10^(-6) cm^(2)`

Explanation

To solve the question regarding the unit "barn" in nuclear chemistry, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of a Barn**:
- A barn is a unit used in nuclear chemistry to measure the reaction cross-sectional area of atomic nuclei and subatomic particles.

2. **Identify the Measurement Unit**:
- Since a barn measures area, it is expressed in square centimeters (cm²).

3. **Know the Value of One Barn**:
- From the information provided, we need to determine the value of one barn in terms of cm².

4. **Evaluate the Options**:
- The question provides four options:
a. \(10^{-24} \, \text{cm}^2\)
b. \(10^{-3} \, \text{cm}^2\)
c. \(10^{-26} \, \text{cm}^2\)
d. \(10^{-6} \, \text{cm}^2\)

5. **Select the Correct Option**:
- Based on the definition and the value of one barn, we conclude that one barn is equal to \(10^{-24} \, \text{cm}^2\). Therefore, the correct answer is option (a).

### Final Answer:
The correct answer is **a. \(10^{-24} \, \text{cm}^2\)**.

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