The paramagnetic species is
 

a) The carbon atom in the carbanion has a negative charge, which implies that one pair of its electrons is not connected to another atom while the other six are. It thus has eight electrons. It has a magnetic field.
b) Carbonium ions have four electrons and a positive charge on the carbon atom. It is diamagnetic as well.
c) A free radical is any molecule belonging to a species that is capable of supporting itself independently and that has an unpaired electron in an atomic orbital. Consequently, it has a paramagnetic character.
Hence, the correct option (C). Free Radical