Question

${}_{18}{\text{Ar}}^{40}$ and ${}_{19}{\text{K}}^{40}$ is called :

• A. isomers
• B. isobars
• C. isotopes
• D. isotones

Answer 1

Answer: (B)

isobars

If two different elements have the same mass number but have a different atomic number, they are known as isobars. In isobars nucleons (protons+neutrons) are equal.

Hence, for $Ar$ and $K$, they have the same atomic mass of 40 but have different an atomic number of 18 and 19 respectively. So, they are isobars.