Question

The atomic number and mass number of an element ${}_{20}{}^{40}\mathrm{Ca}$ is respectively,

• A. 20 and 20
• B. 40 and 20
• C. 20 and 40
• D. 60 and 20

Answer 1

The correct option is C

20 and 40

1. The symbol of an atom can be represented as ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X}$, where X is the atomic symbol, A represents the mass number and Z represents the atomic number.
2. So, In ${}_{20}{}^{40}\mathrm{Ca}$, 20 is the atomic number and 40 is the mass number.

Hence, the correct option is (C) 20 and 40.