Which of the following transformations is not correct ?

Options

A. `_33^75 As +_2^4 He to _35^78 Br +_0^1 n`
B. `_3^7 Li + _1^1 H to _4^7 Be+_0^1 n`
C. `_21^45 Sc+_0^1n to _20^45 Ca+_0^1 n`
D. `_83^209 Bi+_1^2 H to _84^210 Po+_0^1 n`

Answer

To determine which transformation is not correct, we need to analyze each option based on the conservation of atomic number and mass number.

### Step-by-Step Solution:

1. **Understanding the Problem**: We need to check the transformations given in the options and determine which one does not follow the conservation laws of atomic number and mass number.

2. **Analyzing Option A**:
- **Reactant**: Atomic number = 32 + 33 + 235 = 300; Mass number = 75 + 479 = 554.
- **Product**: Atomic number = 35 + 0 = 35; Mass number = 35 + 1 = 36.
- **Conclusion**: The atomic numbers and mass numbers do not match. Thus, this transformation is correct.

3. **Analyzing Option B**:
- **Reactant**: Atomic number = 3; Mass number = 7.
- **Product**: Atomic number = 4; Mass number = 8.
- **Conclusion**: The atomic numbers and mass numbers match. Thus, this transformation is correct.

4. **Analyzing Option C**:
- **Reactant**: Atomic number = 21 + 0 = 21; Mass number = 46.
- **Product**: Atomic number = 20 + 0 = 20; Mass number = 46.
- **Conclusion**: The atomic numbers do not match (21 ≠ 20). Thus, this transformation is *not correct*.

5. **Analyzing Option D**:
- **Reactant**: Atomic number = 83 + 1 = 84; Mass number = 209 + 2 = 211.
- **Product**: Atomic number = 84; Mass number = 210 + 1 = 211.
- **Conclusion**: The atomic numbers and mass numbers match. Thus, this transformation is correct.

6. **Final Conclusion**: The transformation that is not correct is **Option C**.