  The potential of mean torque governing the orientational ordering of
prochiral solutes in the two nematic phases (N and Nx) formed by certain
classes of symmetric achiral bimesogens is formulated and used for the analysis
of existing NMR measurements on solutes of various symmetries dissolved in the
two phases. Three distinct attributes of the solvent phase, namely polarity of
the orientational ordering, chirality of the constituent molecules and spatial
modulation of the local director, are identified as underlying three possible
mechanisms for the generation of chiral asymmetry in the low temperature
nematic phase (Nx). The role and quantitative contribution of each mechanism to
enantiotopic discrimination in the NX phase are presented and compared with the
case of the conventional chiral nematic phase (N*). It is found that polar
ordering is essential for the appearance of enantiotopic discrimination in
small rigid solutes dissolved in the Nx phase and that such discrimination is
restricted to solutes belonging to the point group symmetries $C_s$ and
$C_{2v}$.
