Question

Any chemical element (X) can be represented as ${}_Z{X}^A$ where ‘Z’ is an atomic number and ‘A’ is the mass number. 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. It is given as 20.
So, ${}_Z{X}^A$ for Calcium is ${}_{20}C{a}^{40}$.