When an atom undergoes `beta^(bar)` decay

Options

A. a neutron changes into a proton
B. a proton changes into a neutron
C. a neutron changes into an antiproton
D. a proton changes into an antineutron

Explanation

To solve the question regarding what happens when an atom undergoes beta minus decay, we can break it down into clear steps:

### Step-by-Step Solution:

1. **Understanding Beta Decay**:
- Beta decay is a type of radioactive decay where an unstable nucleus transforms to a more stable configuration by emitting beta particles. There are two types of beta decay: beta minus (β-) decay and beta plus (β+) decay.

2. **Identifying Beta Minus Decay**:
- In beta minus decay, a neutron in the nucleus of an atom is transformed into a proton. This process involves the emission of an electron (which is the beta particle) and an antineutrino.

3. **The Reaction**:
- The reaction can be summarized as:
\[ n \rightarrow p + e^- + \bar{\nu} \]
- Here, \( n \) is a neutron, \( p \) is a proton, \( e^- \) is the emitted electron (beta particle), and \( \bar{\nu} \) is the antineutrino.

4. **Charge Conservation**:
- In beta minus decay, the charge is conserved. A neutron (which has no charge) is converted into a proton (which has a +1 charge), and to balance this change, an electron (which has a -1 charge) is emitted.

5. **Conclusion**:
- Therefore, the correct statement regarding beta minus decay is that a neutron changes into a proton, along with the emission of an electron and an antineutrino.

### Final Answer:
When an atom undergoes beta minus decay, a neutron changes to a proton, and an electron and an antineutrino are emitted.

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