`""_(92)^(238)`U(IIIB) changes to `""_(9)^(234)` Th by emission of `alpha`- particle . Daughter element will be in -

Explanation

To solve the problem of how Uranium-238 (U) changes to Thorium-234 (Th) through alpha decay, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parent Nucleus**:
The parent nucleus is Uranium-238, represented as \( _{92}^{238}U \). This means Uranium has an atomic number of 92 and a mass number of 238.

2. **Understand Alpha Decay**:
In alpha decay, an alpha particle (which is essentially a helium nucleus, \( _{2}^{4}He \)) is emitted from the parent nucleus. The emission of an alpha particle results in a decrease in the atomic number by 2 and a decrease in the mass number by 4.

3. **Calculate the Daughter Nucleus**:
When Uranium-238 undergoes alpha decay:
- The new atomic number will be \( 92 - 2 = 90 \).
- The new mass number will be \( 238 - 4 = 234 \).

Thus, the daughter nucleus can be represented as \( _{90}^{234}Th \).

4. **Identify the Daughter Element**:
The element with atomic number 90 is Thorium (Th). Therefore, after the alpha decay of Uranium-238, the daughter element is Thorium-234.

5. **Determine the Group of the Daughter Element**:
Thorium (Th) belongs to the actinide series in the periodic table, which is often considered in the context of group 3B.

### Final Answer:
The daughter element will be Thorium-234, represented as \( _{90}^{234}Th \), and it belongs to group 3B.

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