# The maximum sum of the number of neutrons and protons in an isotope of hydrogen is

$(a)\;6\qquad(b)\;5\qquad(c)\;4\qquad(d)\;3$

Tritium have 1 proton and 2 neutron in its nucleus.It is maximum and it is 3. It is also called mass number.
Hence (d) is the correct answer.
edited Mar 26