(A) bohr model can not be extended to two or more electron atoms.
(R) each electron in the atom interacts not only with the positively charged nueleus but also with all other electrons.

Options

A. if both assertion and reason are true and reason is the correct explanation of assertion.
B. if both assertion and reason are true but reason is not the correct explanation of assertion.
C. if assertion is true but reason is false.
D. if both assertion and reason are false.

Explanation

To analyze the given statements regarding the Bohr model and its applicability to multi-electron atoms, we can break down the solution step by step:

### Step 1: Understanding the Bohr Model
The Bohr model was developed to explain the behavior of hydrogen-like atoms, which have only one electron. It describes the electron's motion around the nucleus in fixed orbits and quantizes the energy levels.

**Hint:** Recall the basic principles of the Bohr model, including the quantization of energy levels and the circular motion of electrons.

### Step 2: Limitations of the Bohr Model
The assertion states that the Bohr model cannot be extended to two or more electron atoms. This is true because the model does not account for the interactions between multiple electrons.

**Hint:** Consider how the presence of additional electrons would affect the forces acting on each electron.

### Step 3: Interaction Between Electrons
In a multi-electron atom, each electron experiences not only the attractive force from the positively charged nucleus but also repulsive forces from other electrons. This complicates the motion of the electrons and makes it impossible to treat them as independent particles, as assumed in the Bohr model.

**Hint:** Think about how the forces acting on an electron change when other electrons are present.

### Step 4: Conclusion on Assertion and Reason
The reason states that each electron interacts with both the nucleus and other electrons, which is a valid explanation for why the Bohr model cannot be applied to multi-electron systems. Therefore, both the assertion and the reason are correct, and the reason correctly explains the assertion.

**Hint:** Reflect on how the interactions among electrons lead to the failure of the Bohr model in predicting the behavior of multi-electron atoms.

### Final Solution
- **Assertion (A)**: The Bohr model cannot be extended to two or more electron atoms. (True)
- **Reason (R)**: Each electron in the atom interacts not only with the positively charged nucleus but also with all other electrons. (True)
- Conclusion: Both the assertion and reason are correct, and the reason is a correct explanation for the assertion.