If a radical is defined as a molecule with unpaired electrons,then the answer is OH.However,if you take the more general definition(an atom or molecule with unpaired electrons),then OH,O and H are all radicals.
Radicals are molecules that contains at least one unpaired electron. They are formed when a single covalent bond breaks to leave an unpaired electron on each of the two species created by the breaking of the bond.
The answer for the question is OH, OH is an example of a radical, other common examples NH4+, NO3-, etc.
O, and H, are atoms. An atom is the smallest particle of an element that can take part in a chemical reaction.
H2O, is a molecules, A molecules is a substances made of two or more atoms. It is the smallest particle of a chemical element or a compound that has chemical propertie of an element or a compound.
