Question

Which of these is a pair of isobar?

• A. ${}_6{C}^{12},{}_8{O}^{16}$
• B. ${}_6{C}^{13},{}_6{C}^{14}$
• C. ${}_{20}C{a}^{40},{}_{18}A{r}^{40}$
• D. None of these

Answer 1

The correct option is C ${}_{20}C{a}^{40},{}_{18}A{r}^{40}$

Isobars are atoms of different chemical elements that have the same number of nucleons. Isobars differ in atomic number but have the same mass number.

Hence, option C is correct as both elements have the same atomic mass, i.e., 40 but a different atomic number.