Which of the following is not an isotope of hydrogen?
A
protium
B
deuterium
C
tritium
D
helium
Correct Answer: helium
Protium has only 1 proton, deuterium has one proton and 1 neutron whereas tritium has one proton and two neutrons. They are represented by 1H1, 1D2 and 1T3. Helium has 2 protons and two neutrons, hence can’t consider as an isotope. Isotope means having the same number of protons but differ in the number of neutrons.