For which of the following species, Bohr theory is not applicable ?

Options

A. `"Be"^(3+)`
B. `"Li"^(2+)`
C. `"He"^(2+)`
D. H

Explanation

To determine for which of the following species the Bohr theory is not applicable, we need to understand the conditions under which the Bohr model can be used. The Bohr theory is primarily applicable to hydrogen-like species, which are atoms or ions that have only one electron.

### Step-by-Step Solution:

1. **Understand the Bohr Theory Applicability**:
- The Bohr theory is applicable to hydrogen and hydrogen-like species, which means they must have only one electron in their outer shell.

2. **Analyze the Given Options**:
- **Option A: Be tripositive (Be³⁺)**:
- Beryllium (Be) has an atomic number of 4, meaning it has 4 electrons. The tripositive state indicates that it has lost 3 electrons, leaving it with 1 electron. Since it has only one electron, Bohr theory is applicable here.

- **Option B: Li dipositive (Li²⁺)**:
- Lithium (Li) has an atomic number of 3, so it has 3 electrons. The dipositive state means it has lost 2 electrons, leaving it with 1 electron. Therefore, Bohr theory is also applicable here.

- **Option C: He dipositive (He²⁺)**:
- Helium (He) has an atomic number of 2, which means it has 2 electrons. The dipositive state indicates that it has lost both electrons, resulting in 0 electrons remaining. Since there are no electrons left, Bohr theory is not applicable here.

- **Option D: Hydrogen (H)**:
- Hydrogen has an atomic number of 1 and has only 1 electron. Therefore, Bohr theory is applicable here.

3. **Conclusion**:
- The only species among the options where the Bohr theory is not applicable is **He dipositive (He²⁺)**, as it has no electrons left.

### Final Answer:
Bohr theory is not applicable for **He dipositive (He²⁺)**.