For which of the following species, Bohr theory does not apply?

Options

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

Answer

To determine for which species the Bohr theory does not apply, we need to analyze the characteristics of the species listed and understand the limitations of Bohr's model.

### Step-by-Step Solution:

1. **Understanding Bohr's Theory**:
- Bohr's theory is primarily applicable to hydrogen-like atoms or ions, which are systems with a single electron. This includes hydrogen (H), helium ion (He⁺), lithium ion (Li²⁺), and beryllium ion (Be³⁺).

2. **Identifying Single Electron Systems**:
- A single electron system is one where there is only one electron orbiting the nucleus. The Bohr model can accurately describe the energy levels and spectral lines of these systems.

3. **Analyzing the Given Species**:
- If we consider the species:
- Hydrogen (H) - single electron, Bohr theory applies.
- Helium ion (He⁺) - single electron, Bohr theory applies.
- Lithium ion (Li²⁺) - single electron, Bohr theory applies.
- Beryllium ion (Be³⁺) - single electron, Bohr theory applies.
- H⁺ (Hydrogen ion) - has zero electrons, Bohr theory does not apply.

4. **Conclusion**:
- The only species among the options where Bohr's theory does not apply is H⁺, as it has no electrons.

### Final Answer:
Bohr theory does not apply to H⁺ (Hydrogen ion) because it has zero electrons.