Answer: Option (b) is the correct answer.
Explanation:
Atomic number is the sum of only total number of protons present in an element. Whereas mass number or atomic mass is the sum of total number of both protons and neutrons present in an element.
For example, given atom has atomic number is 8. Â And, it is known that atomic mass of O is 16 g/mol.
Therefore, number of neutrons present in it will be calculated as follows.
          Mass number = no. of protons + no. of neutrons
             16 = 8 + no. of neutrons
          no. of neutrons = 16 - 8 Â
                        = 8
Hence, we can conclude that in the given isotope of oxygen-16 there are 8 protons and 8 neutrons.
