`._(4)Be^(7)` captures a K electron into its nucleus .What is the mass number and atomic number of the nuclide formed ?

Explanation

To solve the problem, we need to understand what happens when a beryllium atom captures a K electron into its nucleus.

### Step-by-Step Solution:

1. **Identify the Initial Atomic Structure of Beryllium:**
- Beryllium (Be) has an atomic number of 4, which means it has 4 protons.
- The mass number of beryllium-7 (Be-7) is 7, which means it has 3 neutrons (since mass number = protons + neutrons).

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