Answer-Which of the following is true about isotopes?

Isotopes are defined as elements having same number of protons and different number of neutrons. Since the number of protons is equal to the number of electrons. Therefore, number of electrons are also same in isotopes. Example of isotopes include hydrogen and deuterium. Hydrogen contains 1 proton, 1 neutron and 1 electron whereas deuterium contains 1 proton,2 neutrons and 1 electron. Hence, option B is correct.