The radioactive series whose end product is `._(83)^(209)Bi` is

Options

A. Thorium series
B. Fourier series
C. Actinium series
D. Neptunium series

Explanation

To determine the radioactive series whose end product is \( _{83}^{209}\text{Bi} \) (Bismuth-209), we need to analyze the possible radioactive series and their starting isotopes.

### Step-by-Step Solution:

1. **Identify the Options**: We have four radioactive series to consider:
- Thorium series
- Uranium series (specifically, the Actinium series)
- Neptunium series

2. **Thorium Series**:
- The thorium series starts from \( _{90}^{232}\text{Th} \) (Thorium-232).
- To reach Bismuth-209, we calculate the mass decay:
\[ 232 - 209 = 23 \]
- This means we would need to decay 23 mass units. This is not feasible through a series of alpha and beta decays.

3. **Actinium Series**:
- The actinium series starts from \( _{92}^{235}\text{U} \) (Uranium-235).
- To reach Bismuth-209, we calculate the mass decay:
\[ 235 - 209 = 26 \]
- This would require 6.5 alpha particles, which is not practically possible since we cannot have half a particle.

4. **Neptunium Series**:
- The neptunium series starts from \( _{93}^{237}\text{Np} \) (Neptunium-237).
- To reach Bismuth-209, we calculate the mass decay:
\[ 237 - 209 = 28 \]
- This decay is feasible as it can occur through a series of alpha and beta decays.

5. **Conclusion**:
- The radioactive series whose end product is \( _{83}^{209}\text{Bi} \) is the **Neptunium series**.

### Final Answer:
The radioactive series whose end product is \( _{83}^{209}\text{Bi} \) is the **Neptunium series**.