Polarizability is the ease of distortability of the electron cloud in a molecule.
Polarizability of a molecule depends upon the amount of electrons and distance of electrons from the nuclear charge.
Greater the size of the molecule, greater is the amount of electrons present in it and hence higher is the polarizability.
Among the given pairs of molecules, the pair which is arranged with the particle of higher polarizability listed first is C) because only in this case the species with higher size (hence higher polarizability) is listed first. All the other pairs have bigger molecules listed second.