During `beta^(-)` emission

Options

A. A neutron in the nucleus decays emitting an electron
B. An electron already present within the nucleus is ejected
C. A part of the binding energy of the nucleus is converted into an electron
D. A proton in the nucleus decays emitting an electron

Answer

### Step-by-Step Solution:

1. **Understanding Beta Minus Emission**:
- Beta minus (β-) emission is a type of radioactive decay in which a neutron in an unstable nucleus is transformed into a proton.
- During this process, an energetic electron (beta particle) and an antineutrino are emitted.

2. **Nuclear Reaction Representation**:
- Let's represent the process with a generic element:
- Before decay: \( \text{X} \) (with mass number \( A \) and atomic number \( Z \))
- After decay: The element transforms into a new element \( \text{Y} \) (with the same mass number \( A \) and atomic number \( Z+1 \)).
- The reaction can be summarized as:
\[ n \rightarrow p + e^- + \bar{\nu} \]
- Here, \( n \) is the neutron, \( p \) is the proton, \( e^- \) is the emitted electron, and \( \bar{\nu} \) is the antineutrino.

3. **Conservation of Mass Number**:
- The mass number \( A \) remains unchanged because the total number of nucleons (protons + neutrons) does not change.
- The atomic number \( Z \) increases by 1 because one neutron is converted into one proton.

4. **Conclusion**:
- The main outcome of beta minus emission is that a neutron is converted into a proton, an electron is emitted, and the atomic number of the element increases by 1 while the mass number remains the same.

### Final Answer:
The correct statement regarding beta minus emission is:
- A neutron in the nucleus decays emitting an electron.

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