`C-14` is formed in the upper atmosphere. Why it does not occur at the ground level ?

Explanation

### Step-by-Step Solution:

1. **Understanding C-14**:
- C-14, or Carbon-14, is an isotope of carbon. It has 6 protons and 8 neutrons, giving it a mass number of 14.

2. **Formation of C-14**:
- C-14 is formed in the atmosphere through a nuclear reaction involving nitrogen. Specifically, nitrogen-14 (which has an atomic number of 7 and a mass number of 14) absorbs a thermal neutron.

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