A: Bohr's model with its planet - like electron is not applicable to many electron atoms.
R: Unlike the situation in the solar system, where planet-planet gravitational forces are very small as compared to the gravitational force of the sun on each planet, the electron electric force interaction is comparable in magnitude to the electron nucleus electric force.

Options

A. If both Assertion & Reason are true and the reason is the correct explantion of the assertion , then mark (1)
B. if both Assertion & Reason are true but the reason is not the correct explantion of the assertion , then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the assertion and reason question, we need to analyze both statements and determine their validity.

### Step 1: Analyze the Assertion
- **Assertion (A)**: "Bohr's model with its planet-like electron is not applicable to many electron atoms."
- **Explanation**: Bohr's model was primarily developed for the hydrogen atom, which has only one electron. In multi-electron atoms, the interactions between electrons become significant, and the simplifications made in Bohr's model are no longer valid. Therefore, the assertion is **correct**.

### Step 2: Analyze the Reason
- **Reason (R)**: "Unlike the situation in the solar system, where planet-planet gravitational forces are very small as compared to the gravitational force of the sun on each planet, the electron electric force interaction is comparable in magnitude to the electron nucleus electric force."
- **Explanation**: In the solar system, the gravitational force between planets is negligible compared to the gravitational force exerted by the sun. However, in an atom, the electric forces between electrons (which repel each other) and the electric force between the nucleus and the electrons (which attract them) are of comparable strength. This makes the interactions between electrons significant in multi-electron systems. Thus, the reason is also **correct**.

### Step 3: Conclusion
- Both the assertion and the reason are correct, and the reason correctly explains the assertion. Therefore, the relationship between the two statements is valid.

### Final Answer
Both the assertion (A) and the reason (R) are correct, and R is the correct explanation of A.

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