Question

Which of the following pairs is an isobar?

• A. \( ^1H \) and \( ^2H \)
• B. \( ^2H \) and \( ^3H \)
• C. \( ^{13}C \) and \( ^{12}C \)
• D. \( ^{18}Ar \) and \( ^{40}K \)

Hint:

Isobars are elements with the same mass number but different atomic numbers.

Answer 1

The Correct Option is C

Step 1: Understanding the concept.
Isobars are atoms of different elements that have the same mass number. The mass number is the sum of protons and neutrons.
Step 2: Analyzing the options.
(1) \( ^1H \) and \( ^2H \): This is incorrect. These are isotopes of hydrogen, not isobars, because they have different mass numbers.
(2) \( ^2H \) and \( ^3H \): This is incorrect. These are isotopes of hydrogen, with different mass numbers.
(3) \( ^{13}C \) and \( ^{12}C \): Correct. These are isotopes of carbon, but they are not isobars since they have different numbers of neutrons but the same mass number (13 and 12).
(4) \( ^{18}Ar \) and \( ^{40}K \): This is incorrect. These are not isobars as they have different mass numbers.
Step 3: Conclusion.
The correct answer is (3) \( ^{13}C \) and \( ^{12}C \), which are isobars as they share the same mass number.