Assertion `(A):` `._(92)U^(238) (IIIB)overset(-alpha)rarrAoverset(-alpha)rarrB overset(-beta)rarrC`
Reason `(R):` Element `B` will be of `II A ` group.

Answer

To solve the given question, we will analyze the assertion and reason step by step.

### Step 1: Understand the Assertion
The assertion states that Uranium-238 (U-238) undergoes a series of radioactive decays:
1. U-238 emits an alpha particle (α) to form element A.
2. Element A emits another alpha particle to form element B.
3. Element B emits a beta particle (β) to form element C.

### Step 2: Determine the Products of Each Decay
1. **Decay of U-238:**
- Atomic number of U-238 = 92
- Mass number of U-238 = 238
- When U-238 emits an alpha particle (which has an atomic number of 2 and mass number of 4):
- New atomic number = 92 - 2 = 90
- New mass number = 238 - 4 = 234
- Therefore, element A is Thorium-234 (Th-234), which has atomic number 90.

2. **Decay of Element A (Th-234):**
- Th-234 emits another alpha particle:
- New atomic number = 90 - 2 = 88
- New mass number = 234 - 4 = 230
- Therefore, element B is Radium-230 (Ra-230), which has atomic number 88.

3. **Decay of Element B (Ra-230):**
- Ra-230 emits a beta particle:
- New atomic number = 88 + 1 = 89
- Mass number remains the same = 230
- Therefore, element C is Actinium-230 (Ac-230), which has atomic number 89.

### Step 3: Analyze the Reason
The reason states that element B will be of the 2nd A group (Group 2) in the periodic table.
- We found that element B is Radium (Ra), which belongs to Group 2 (IIA) in the periodic table.

### Conclusion
- Both the assertion and reason are correct statements:
- Assertion (A) is correct: U-238 decays to form A, then B, and then C.
- Reason (R) is correct: Element B (Radium) is indeed in Group 2 (IIA).
- However, the reason does not directly explain the assertion, as it only states the group of element B without explaining the decay process.

### Final Answer
The correct option is **B**: Both assertion and reason are correct, but the reason is not the correct explanation of the assertion.

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