The period number in the long form of the periodic table is equal to

Options

A. magnetic quantum number of any element of the period
B. atomic number of any element of the period
C. maximum principal quantum number of any element of the period
D. maximum azimuthal quantum number of any element of the period

Explanation

To solve the question regarding what the period number in the long form of the periodic table is equal to, we will analyze the options provided and relate them to the concept of quantum numbers.

### Step-by-Step Solution:

1. **Understanding Periods in the Periodic Table**:
- The periodic table is organized into rows called periods. Each period corresponds to the filling of electron shells in atoms.

2. **Identifying Quantum Numbers**:
- There are four types of quantum numbers that describe the properties of electrons in atoms:
- Principal Quantum Number (n)
- Azimuthal Quantum Number (l)
- Magnetic Quantum Number (m)
- Spin Quantum Number (s)

3. **Relating Periods to Quantum Numbers**:
- The principal quantum number (n) indicates the main energy level or shell of an electron in an atom. The value of n corresponds directly to the period number in the periodic table.
- For example, elements in the first period have n=1, elements in the second period have n=2, and so on.

4. **Evaluating the Options**:
- **Magnetic Quantum Number**: This describes the orientation of orbitals and does not relate to the period number.
- **Atomic Number**: This is the number of protons in an atom and varies across the periodic table but does not define the period.
- **Maximum Principal Quantum Number**: This corresponds to the highest energy level occupied by electrons in a given period, which is indeed equal to the period number.
- **Maximum Azimuthal Quantum Number**: This relates to the shape of orbitals and does not define the period.

5. **Conclusion**:
- The period number in the long form of the periodic table is equal to the **maximum principal quantum number** of any element in that period. Therefore, the correct answer is the third option.

### Final Answer:
The period number in the long form of the periodic table is equal to the **maximum principal quantum number** of any element of the period.

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