A nucleus undertgoes `beta`-decay. How does its (i) mass number (ii) atomic number change ?

Explanation

To solve the question about how a nucleus changes during beta decay, we will analyze the changes in both the mass number and the atomic number.

### Step-by-Step Solution:

1. **Understanding Beta Decay**:
- Beta decay is a type of radioactive decay in which a nucleus emits a beta particle. A beta particle can be an electron (β-) or a positron (β+). In this case, we will focus on β- decay, which is more common.

2. **Effect on Mass Number**:
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