The answer is B. H-2
Considering H-2, hydrogen has 1 proton and 2 nucleon. The number of neutron is obtained by nucleon number - proton number. Here the neutron number is 2 - 1 = 1 neutron. Applying the same logic with others choices to see which one is the right answer. So, B is the right answer. Hoped i helped...
Take another example : Al (aluminium) has 13 protons and 27 nucleon. Find the proton, electron and neutron numbers.
proton number = 13
electron number = proton number = 13
neutron number = nucleon number - proton number = (27 - 13) = 14
