Assertion (A ): Bohr model is not applicable for multi-electron model.
Reason (R ): Bohr model cannot account for sublevel (s, p, d,f) orbitals and electron spin.

Options

A. Both A and R are true and R is the correct explanation of A
B. Both A and R are true but R is NOT the correct explanation of A
C. A is true but R is false
D. A is false and R is true

Explanation

To analyze the assertion and reason provided in the question, we will break down the statements and evaluate their validity step by step.

### Step 1: Understand the Assertion
**Assertion (A)** states that the Bohr model is not applicable for multi-electron atoms.

- The Bohr model was primarily developed to explain the hydrogen atom, which has only one electron. It successfully describes the quantized energy levels of hydrogen.
- When it comes to multi-electron atoms (like helium, lithium, etc.), the interactions between multiple electrons complicate the energy levels and their arrangements. The Bohr model does not account for these interactions, which is why it fails for multi-electron systems.

### Step 2: Understand the Reason
**Reason (R)** states that the Bohr model cannot account for sub-levels (s, p, d, f) and electron spin.

- The Bohr model simplifies the atom to a nucleus with electrons moving in fixed orbits. It does not incorporate the concept of sub-levels, which are essential for understanding the arrangement of electrons in multi-electron atoms.
- Additionally, the Bohr model does not consider electron spin, a fundamental property of electrons that affects their behavior and arrangement in an atom.

### Step 3: Evaluate the Truth of Assertion and Reason
- Both the assertion and the reason are true. The Bohr model is indeed not applicable to multi-electron atoms, and it fails to account for sub-levels and electron spin.

### Conclusion
- Therefore, both the assertion (A) and the reason (R) are true, and the reason correctly explains why the assertion is true.

### Final Answer
- Assertion (A) is true: The Bohr model is not applicable for multi-electron atoms.
- Reason (R) is true: The Bohr model cannot account for sub-levels (s, p, d, f) and electron spin.

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