Which are isotopes? an atom that has an atomic number of 20 and a mass number of 42 is an isotope of an atom that has which are isotopes? an atom that has an atomic number of 20 and a mass number of 42 is an isotope of an atom that has an atomic number of 20 and a mass number of 40. an atomic number of 21 and a mass number of 42. 22 protons and 20 neutrons. 22 neutrons and 20 protons?

Explanation:

Isotopes are defined as the species which contain same number of protons but different number of neutrons.

As the sum of all the protons present in an atom is known as atomic number. Whereas the sum of total number of protons and neutrons is known as atomic mass.

Hence, isotopes are also defined as atoms with same atomic number but different atomic mass.

For example, an atom that has an atomic number of 20 and a mass number of 42 will contain the following number of neutrons.

                 Mass number = no. of protons + no. of neutrons

                            42 = 20 + no. of neutrons

                 no. of neutrons = 42 - 20

                                            = 22

So, isotope of this atom could be . This means that an element with atomic number of 20 and a mass number of 40.

Thus, we can conclude that an atom that has an atomic number of 20 and a mass number of 42 is an isotope of an atom that has an atomic number of 20 and a mass number of 40.

Since, both of them contains same number of protons but different number of neutrons.