Question

Any chemical element (X) can be represented as ${}_Z{X}^A$ where ‘Z’ is the atomic number and ‘A’ is the mass number. The atomic number refers to the number of protons and the mass number refers to the sum of protons and neutrons in an atom. For an element, calcium which has 20 protons and 20 neutrons, identify the correct representation:

• A. ${}_{20}C{a}^{40}$
• B. ${}_{40}C{a}^{20}$
• C. ${}_{20}C{a}^{20}$
• D. ${}_{20}C{a}^{60}$

Answer 1

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

The mass number of an atom is the sum of protons (p) and neutrons (n). Given, Calcium has 20 protons and 20 neutrons.
So, mass number (A) of Calcium = p + n = 20 + 20 = 40. Hence, A = 40.
Atomic number is the number of protons. Hence, Z = 20.
So, ${}_Z{X}^A$ for Calcium is ${}_{20}C{a}^{40}$.