Which of these is a pairs of isobar

Options

A. `6^(C^(12)) , 8^(O^(16))`
B. `6^(C^(13)) , 6^(O^(14))`
C. `20^(Ca^(40)) , 18^(Ar^(10))`
D. `20^(Ca^(40)) , 18^(Ar^(10))`

Answer

To determine which of the given pairs is a pair of isobars, we need to follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Isobars**:
- Isobars are atoms of different elements that have the same mass number (A) but different atomic numbers (Z). This means they have the same total number of nucleons (protons + neutrons) but differ in the number of protons.

2. **Identify the Mass Numbers in Each Option**:
- Check the mass numbers (A) of the elements provided in each option.

3. **Compare Mass Numbers**:
- For each pair of elements, compare their mass numbers. If the mass numbers are not the same, they cannot be isobars.

4. **Check Atomic Numbers**:
- If the mass numbers are the same, check the atomic numbers (Z) of the elements. They should be different for the pair to qualify as isobars.

5. **Evaluate the Options**:
- Go through each option systematically:
- **Option 1**: Check if the mass numbers are the same.
- **Option 2**: Check if the mass numbers are the same.
- **Option 3**: Check if the mass numbers are the same.
- **Option 4**: Check if the mass numbers are the same.

6. **Identify the Correct Pair**:
- From the analysis, identify which option has the same mass number but different atomic numbers.

7. **Conclusion**:
- The correct answer will be the option where the mass number is the same and the atomic numbers are different.

### Example Analysis:
- **Option 3**:
- 20Ca40 (Calcium with mass number 40) and 18Ar40 (Argon with mass number 40).
- Both have a mass number of 40 (A = 40) but different atomic numbers (Z = 20 for Calcium and Z = 18 for Argon).
- Therefore, they are isobars.

### Final Answer:
- The pair of isobars is **20Ca40 and 18Ar40**.

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