Assertion: Helium and beryllium have similar outer electronic configuration of the type `ns^(2)`.
Reason: Both are chemically inert.

Options

A. If both Assertion (A) and (R ) are correct and Reason (R ) is the correct explanation of Assertion (A).
B. If both (A) and (R ) are correct but (R ) is not the correct explanation for (A).
C. If (A) is correct but (R ) is not correct.
D. If (A) and (R ) are correct

Explanation

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

### Step 1: Analyze the Assertion
The assertion states that "Helium and beryllium have similar outer electronic configuration of the type `ns^(2)`."

- **Helium (He)** has an atomic number of 2, and its electronic configuration is `1s²`. The outer electronic configuration can be considered as `ns²`, where n=1 (since it only has one shell).
- **Beryllium (Be)** has an atomic number of 4, and its electronic configuration is `1s² 2s²`. The outer electronic configuration is `2s²`, which can also be represented as `ns²`, where n=2.

Thus, both helium and beryllium can be said to have an outer electronic configuration of the type `ns²`. Therefore, the assertion is **correct**.

### Step 2: Analyze the Reason
The reason states that "Both are chemically inert."

- **Helium** is indeed a noble gas and is chemically inert due to its complete outer shell (1s²).
- **Beryllium**, on the other hand, is not chemically inert. It has a complete 2s subshell (2s²), but it is reactive because it can lose its two valence electrons to achieve a stable electronic configuration similar to that of noble gases.

Thus, while helium is chemically inert, beryllium is not. Therefore, the reason is **incorrect**.

### Conclusion
Since the assertion is correct but the reason is incorrect, the correct answer is option **C**: "A is correct and R is not correct."