The principal quantum number, n describes

Options

A. Shape of orbital
B. Sub-shell of electron
C. Main energy shell of electron
D. Spin of electron

Explanation

To answer the question "The principal quantum number, n describes:", we need to analyze the options provided and understand what the principal quantum number signifies in atomic structure.

### Step-by-Step Solution:

1. **Understanding Quantum Numbers**: Quantum numbers are used to describe the properties of atomic orbitals and the electrons in those orbitals. There are four quantum numbers: principal (n), azimuthal (l), magnetic (m), and spin (s).

2. **Identifying the Principal Quantum Number (n)**: The principal quantum number, denoted as 'n', indicates the main energy level or shell of an electron in an atom. It can take positive integer values (n = 1, 2, 3, ...).

3. **Energy Levels and Distance**: The value of 'n' determines the distance of the electron from the nucleus. For example, when n = 1, the electron is closest to the nucleus, and as n increases, the electron is found further away from the nucleus.

4. **Correct Option**: Among the options provided:
- **Shape of orbital**: This is described by the azimuthal quantum number (l).
- **Sub-cell of electron**: Also described by the azimuthal quantum number (l).
- **Main energy cell of electron**: This is indeed described by the principal quantum number (n).
- **Spin of electron**: This is described by the spin quantum number (s).

5. **Conclusion**: Therefore, the principal quantum number 'n' describes the main energy cell of the electron.

### Final Answer:
The principal quantum number, n, describes the **main energy cell of electron**.

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