The uranium (mass no. 238 and at no. 92) emits an `alpha`-particle, the product has the mass no. and at .no:

Options

A. 236 and 92
B. 234 and 90
C. 238 and 90
D. 236 and 90

Answer

To solve the problem, we need to determine the mass number and atomic number of the product formed when uranium (with mass number 238 and atomic number 92) emits an alpha particle.

### Step-by-Step Solution:

1. **Understand the emission of an alpha particle**:
An alpha particle consists of 2 protons and 2 neutrons. When an element emits an alpha particle, it loses these 4 nucleons (2 protons + 2 neutrons).

2. **Identify the initial values**:
- Mass number of Uranium (U) = 238
- Atomic number of Uranium (U) = 92

3. **Calculate the new mass number**:
- New mass number = Initial mass number - Mass number of alpha particle
- The mass number of an alpha particle = 4 (since it has 2 protons and 2 neutrons).
- New mass number = 238 - 4 = 234

4. **Calculate the new atomic number**:
- New atomic number = Initial atomic number - Atomic number of alpha particle
- The atomic number of an alpha particle = 2 (because it has 2 protons).
- New atomic number = 92 - 2 = 90

5. **Identify the new element**:
- The new element formed after the emission of the alpha particle will have:
- Mass number = 234
- Atomic number = 90
- The element with atomic number 90 is Thorium (Th).

### Final Answer:
The product formed after uranium (mass number 238, atomic number 92) emits an alpha particle has:
- Mass number = 234
- Atomic number = 90