Which of the following is not a part of isotopes?

Options

A. `""_(6)^(12)X,""_(6)^(13)Y`
B. `""_(17)^(35)X,""_(17)^(37)Y`
C. `""_(6)^(14)X,""_(7)^(14)Y`
D. `""_(4)^(8)X,""_(4)^(9)Y`

Explanation

To determine which of the given options is not a part of isotopes, we need to understand the definition of isotopes. Isotopes are variants of a particular chemical element that have the same number of protons (atomic number) but different numbers of neutrons, which results in different mass numbers.

### Step-by-Step Solution:

1. **Understand the Definition of Isotopes**:
- Isotopes are atoms of the same element that have the same atomic number but different mass numbers.
- This means they have the same number of protons but a different number of neutrons.

2. **Analyze the Options**:
- We need to check each option to see if it has the same atomic number but different mass numbers.

3. **Option 1**:
- If the atomic number is 6 (for example, Carbon), and the mass numbers are different (e.g., Carbon-12 and Carbon-14), then this is an example of isotopes.

4. **Option 2**:
- If the atomic number is the same but the mass numbers are different (e.g., Oxygen-16 and Oxygen-18), this is also an example of isotopes.

5. **Option 3**:
- If the atomic number is different (for example, one element has an atomic number of 6 and another has an atomic number of 8), even if the mass numbers are the same, these cannot be isotopes. They are different elements.

6. **Conclusion**:
- Since isotopes must have the same atomic number, the option where the atomic number is different is not a part of isotopes. Therefore, the correct answer is **Option 3**.

### Final Answer:
**Option 3** is not a part of isotopes.