Question

why is the mass of nucleus of hydrogen atom is smaller than the addition mass of proton and neutron

Answer 1

because there is no nuetrons in the hydrogen nucleus there is only one proton...Hence it is simple that the mass of proton must be less than the mass of nuetron aand proton......but there are some speicies of hydrogen in which we can find nuetron and those spiecies are dutarium and tritium ...we can find 1 and 2 nuetrons respectively in them.....i hope u have got all the info that u needed for hydrogen nucleus...

Answer 2

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The actual mass is always less than the sum of the individual masses of the constituent protons and neutrons because energy is removed when when the nucleus is formed. This energy has mass, which is removed from the total mass of the original particles.