# Neutron is not present in the nucleus of

$\begin{array}{1 1}(a)\;\text{Helium}\\(b)\;\text{Protium}\\(c)\;\text{Tritium}\\(d)\;\text{Lithium}\end{array}$

Neutron is not present in the nucleus of protium.
Protium is the normal hydrogen $(1H^1)$ which is having one proton and no neutrons.
Hence (b) is the correct answer.
edited Nov 25, 2017