Bohr theory is not applicable for

Options

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

Answer

To determine where the Bohr theory is not applicable, we need to analyze the options given in the question. The Bohr theory is primarily applicable to hydrogen-like atoms, which are atoms that have only one electron. Here’s a step-by-step breakdown:

### Step 1: Understand the Bohr Theory
- The Bohr theory is a model of the atom that describes the behavior of electrons in hydrogen-like atoms (atoms with only one electron).
- It is based on quantized energy levels, which means that electrons can only occupy certain allowed energy levels.

**Hint:** Remember that Bohr's model works best for systems with a single electron.

### Step 2: Analyze Each Option
- **Option 1: Helium ion (He⁺)**
- Helium has an atomic number of 2, meaning it has 2 protons and normally 2 electrons. However, He⁺ has lost one electron, leaving it with only one electron.
- Since He⁺ is a hydrogen-like atom, Bohr theory is applicable here.

**Hint:** Check if the species has only one electron.

- **Option 2: Lithium ion (Li²⁺)**
- Lithium has an atomic number of 3, meaning it has 3 protons and normally 3 electrons. Li²⁺ has lost two electrons, leaving it with one electron.
- Like He⁺, Li²⁺ is also a hydrogen-like atom, so Bohr theory is applicable.

**Hint:** Again, confirm the number of electrons in the ion.

- **Option 3: Bromine ion (Br⁺)**
- Bromine has an atomic number of 35, which means it has 35 protons and normally 35 electrons. Br⁺ is a multi-electron system with many electrons.
- Since it has multiple electrons, Bohr theory is not applicable here.

**Hint:** Multi-electron systems typically do not follow Bohr's model.

- **Option 4: Hydrogen atom (H)**
- Hydrogen has an atomic number of 1 and has only one electron. Therefore, Bohr theory is applicable to hydrogen.

**Hint:** Hydrogen is the simplest atom and fits perfectly into Bohr's model.

### Step 3: Conclusion
- Based on the analysis, the only option where the Bohr theory is not applicable is **Option 3: Bromine ion (Br⁺)**, as it is a multi-electron system.

**Final Answer:** Bohr theory is not applicable for **Bromine ion (Br⁺)**.