However, the linear correlation of the refractive index with xdic is not as accurate as in the case of density; the R 2 value is equal to 0.888 (Fig. ). It should be noted here that the experimental values for DSILs containing similar or the same proportion of MCPA anions as dicamba (AB0.4-AB0.6) were close to the theoretical ones. Thus, the relationship between ΔnD 20 and xdic followed a similar pattern as the dependence of excess molar volume (Vm E20 ) on the molar fraction of dicamba. This corroborates with a known relationship between density and refractive index: with a higher density of a substance, the spatial packing of its chemical constituents increases, and refraction results from the interaction of light with molecules (or ions).