Calculate the number of neutrons in the following element:

${}_{20}{}^{40}\mathrm{Ar}$

For any element X, mass number and atomic number is represented as ${}_{\mathrm{Atomic}\mathrm{number}}{}^{\mathrm{Mass}\mathrm{number}}\mathrm{X}$

$Numberofneutrons=Massnumber-Numberofprotons$

Step-1: Calculate the mass number of Argon (Ar)

• For ${}_{20}{}^{40}\mathrm{Ar}$, Mass number = 40

Step-2: Calculate the number of protons

• Number of protons in an atom = Atomic number of that element
• From ${}_{20}{}^{40}\mathrm{Ar}$, Atomic number = 20 (Given)
• Therefore, Number of protons = 20

Step-3: Calculate the number of neutrons

• Substituting the values of mass number and number of protons in the above formula
• Number of neutrons = 40- 20 = 20
• Number of neutrons = 20