The atomic number of an element is 22 and its mass number is 40. The correct order representing the number of electrons, protons and neutrons respectively in this atom is:
The correct option is D 22, 22, 18
As we know,
the atomic number is defined as the total number of protons present in the nucleus of an atom. Therefore the number of protons in the atom is 18, also number of protons is equal to number of electrons , hence number of electectrons is also equal to 18.
The mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom.
Mass number = Total number of protons + Total number of neutrons
Therefore, Total number of neutrons = 40 - 18 = 22