Molar conductivity of transition metal complexes solutions
Charge transport depends on the presence of charge carriers, and an increase of the concentration of charge carriers may increase the electric conductivity.  This is the basis of the answer given to you which (implicitly) assumes each of these complexes dissociate, e.g.

$\ce{K4[Fe(CN)6] &lt;=&gt; 4 K+ + [Fe(CN)6]^{4-}}$

in your solvent completely.  In this view, charge transport happenz without moving these carriers on a macroscopic level (like  the salt bridge used to connect electrochemical cells). You may imagine a bucket brigade, instead people exchanging buckets of water, ions shuttle electrons.

On the other hand, there are examples where charge transport is coupled to the transport of matter (e.g., ions) on a macroscopic scale.  Proteins and nucleic acids, for example, may be separated by this (e.g., gel electrophoresis); their different size (and shape, and charge) quite noticeably influence how quickly they travel in an electric field.