Isotopes of hydrogen
(a) Hydrogen (protium) 11H
No. of protons = 1
No. of electrons = 1
No. of neutrons 1 – 1 = 0
(b) Deutrium 21H
No. of protons = 1
No. of electrons = 1
No. of neutrons = 2 – 1 = 1
(c) Tritium 31H
No. of protons = 1
No. of electrons = 1
No. of neutrons = 3 – 1 = 2.