Which among the following `"is"//"are"` fissible?

Options

A. `._(92)U^(235)`
B. `._(92)U^(238)`
C. `._(94)Pu^(239)`
D. `._(94)Pu^(238)`

Answer

To determine which among the given isotopes are fissile, we need to analyze each option based on their ability to undergo fission with slow-moving neutrons.

### Step-by-Step Solution:

1. **Understanding Fissile Materials**:
- Fissile materials are those that can sustain a nuclear fission chain reaction when bombarded with neutrons. They can react with slow-moving (thermal) neutrons without requiring additional energy.

2. **Analyzing Uranium-235 (U-235)**:
- U-235 is known to be fissile. It can readily undergo fission when it absorbs a slow-moving neutron, leading to a chain reaction. Therefore, U-235 is fissile.

3. **Analyzing Uranium-238 (U-238)**:
- U-238 is not fissile with slow-moving neutrons. It requires fast-moving neutrons to undergo fission, which means it cannot sustain a chain reaction on its own with thermal neutrons. Thus, U-238 is not fissile.

4. **Analyzing Plutonium-239 (Pu-239)**:
- Pu-239 is also fissile. Similar to U-235, it can react with slow-moving neutrons and sustain a fission chain reaction. Therefore, Pu-239 is fissile.

5. **Analyzing Plutonium-238 (Pu-238)**:
- Pu-238 behaves like U-238; it requires fast-moving neutrons to undergo fission and cannot sustain a chain reaction with thermal neutrons. Hence, Pu-238 is not fissile.

### Conclusion:
Based on the analysis:
- **Fissile Isotopes**: U-235 and Pu-239.
- **Non-fissile Isotopes**: U-238 and Pu-238.

Thus, the correct answer is that **Uranium-235 and Plutonium-239 are fissile**.