When `U^235` is bombarded with one neutron, the fission occurs and the products are three neutrons, `,_36 Kr^94` and.

Options

A. `""_(56)Ba^(141)`
B. `""_(54)Xe^(139)`
C. `""_(56)Ba^(139)`
D. `""_(58)I^(142)`

Answer

To solve the problem, we need to analyze the fission reaction of Uranium-235 when it is bombarded with a neutron. The reaction can be summarized as follows:

1. **Identify the initial and final components of the reaction**:
- Initial: Uranium-235 (U-235) + 1 neutron
- Final: 3 neutrons + Krypton-94 (Kr-94) + another unknown atom (let's denote it as X).

2. **Write down the mass numbers and atomic numbers**:
- The mass number of U-235 is 235, and its atomic number (Z) is 92.
- The mass number of the neutron is 1, and its atomic number is 0.
- The mass number of Kr-94 is 94, and its atomic number is 36.
- Let the mass number of the unknown atom X be A and its atomic number be Z.

3. **Set up the mass number equation**:
- Before the reaction: Mass number = 235 (U-235) + 1 (neutron) = 236
- After the reaction: Mass number = 94 (Kr-94) + 3 (neutrons) + A
- Therefore, we can write the equation:
\[ 236 = 94 + 3 + A \]
- Simplifying gives:
\[ 236 = 97 + A \implies A = 236 - 97 = 139 \]

4. **Set up the atomic number equation**:
- Before the reaction: Atomic number = 92 (U-235)
- After the reaction: Atomic number = 36 (Kr-94) + Z
- Therefore, we can write the equation:
\[ 92 = 36 + Z \]
- Simplifying gives:
\[ Z = 92 - 36 = 56 \]

5. **Identify the unknown atom**:
- The unknown atom has a mass number of 139 and an atomic number of 56.
- Referring to the periodic table, the element with atomic number 56 is Barium (Ba).

6. **Conclusion**:
- The unknown atom formed in the fission reaction is Barium-139 (Ba-139).

### Final Answer:
The unknown atom formed is **Barium-139 (Ba-139)**.