Bohr's theory is not applicable to

Options

A. H
B. `He^(+)`
C. `Li^(2+)`
D. `H^(+)`

Answer

To determine where Bohr's theory is not applicable, we need to analyze each option based on the number of electrons present in the species.

### Step-by-Step Solution:

1. **Understanding Bohr's Theory**:
- Bohr's theory is applicable to hydrogen-like species, which means it can only be applied to systems with a single electron (mono-electronic systems).

2. **Analyzing the Options**:
- **Option 1: Hydrogen (H)**
- Hydrogen has 1 electron. Since it is a mono-electronic system, Bohr's theory is applicable.
- **Option 2: Helium Plus (He⁺)**
- Helium has 2 electrons. When one electron is removed (He⁺), it has 1 electron left. Thus, it is also a mono-electronic system, making Bohr's theory applicable.
- **Option 3: Lithium Plus 2 (Li²⁺)**
- Lithium has 3 electrons. When two electrons are removed (Li²⁺), it has 1 electron left. Therefore, it is a mono-electronic system, and Bohr's theory is applicable.
- **Option 4: Hydrogen Plus (H⁺)**
- Hydrogen has 1 electron. When the electron is removed (H⁺), it has no electrons left. Since there are no electrons, Bohr's theory cannot be applied.

3. **Conclusion**:
- The only option where Bohr's theory is not applicable is **Hydrogen Plus (H⁺)**, as it has no electrons.

### Final Answer:
The correct option is **Hydrogen Plus (H⁺)**.

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