Assertion:In the present form of periodic table,the period number corresponds to the highest principal quantum number of the elements in the period.
Reason:Elements having similar outer electronic configuration in their atoms belongs to same period.

Options

A. If both assertion and reason is the correct explanation of assertion.
B. If both assertion and reason is the correct explanation of assertion.
C. If both assertion and reason is the correct explanation of assertion.
D. If both assertion and reason is the correct explanation of assertion.

Explanation

To solve the assertion-reason question, we need to analyze both the assertion and the reason separately.

### Step 1: Analyze the Assertion
The assertion states: "In the present form of the periodic table, the period number corresponds to the highest principal quantum number of the elements in the period."

- **Understanding Principal Quantum Number (n)**: The principal quantum number (n) indicates the energy level of an electron in an atom. The period number in the periodic table reflects the highest energy level that is occupied by electrons in the elements of that period.

- **Example**: In the second period, the elements are Lithium (Li) to Neon (Ne). The electronic configurations are:
- Li: 1s² 2s¹ (highest n = 2)
- Ne: 1s² 2s² 2p⁶ (highest n = 2)

All elements in the second period have their outermost electrons in the n=2 level. Therefore, the assertion is **true**.

### Step 2: Analyze the Reason
The reason states: "Elements having similar outer electronic configuration in their atoms belong to the same period."

- **Understanding Electronic Configuration**: Elements that have similar outer electronic configurations actually belong to the same group (column) in the periodic table, not the same period (row).

- **Example**: In Group 1 (alkali metals), elements like Lithium (Li), Sodium (Na), and Potassium (K) have the following electronic configurations:
- Li: 1s² 2s¹
- Na: 1s² 2s² 2p⁶ 3s¹
- K: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

All these elements have one electron in their outermost shell, which is characteristic of Group 1 elements. Thus, the reason is **false**.

### Conclusion
- **Assertion**: True
- **Reason**: False

Thus, the correct answer is that the assertion is true, and the reason is false.