Question

Which of the following pairs represents isobars?

• A. \(^3\text{He}_2\) and \(^4\text{He}_2\)
• B. \(^{24}\text{Mg}_{12}\) and \(^{25}\text{Mg}_{12}\)
• C. \(^{40}\text{K}_{19}\) and \(^{40}\text{Ca}_{20}\)
• D. \(^{40}\text{K}_{19}\) and \(^{39}\text{K}_{19}\)

Hint:

Isobars have the same mass number but different atomic numbers.

Answer 1

The Correct Option is C

Step 1: Idea:
Compare the superscripts first, since isobars have equal mass numbers.

Step 2: Result:
Only pair C has equal mass numbers ($40$ and $40$) with different atomic numbers ($19$ and $20$).

Final Answer:
The isobars are $^{40}\text{K}_{19}$ and $^{40}\text{Ca}_{20}$, option (C). \[ \boxed{^{40}\text{K}_{19}\ \text{and}\ ^{40}\text{Ca}_{20}} \]