Substituted nitrobenzene, a toxic series of molecules with its wide application in pesticides needs to be removed by a suitable sorbent, whose characteristic is to be determined using the reactivity index theory within the helm of the density-functional theory and as well inside the broad subject range of the hard-soft acid-base (HSAB) principle. We studied a series of meta- and para-substituted nitrobenzene molecules (NBMs) starting from - NH2, -OH, -OCH3, -CHO, -OCOCH3, - COCH3, -CF3, -CN, and -COOCH3 to monitor the effect of electrophilicity and nucleophilicity in their adsorption properties. From the values of the local softness and the charge on the hydrogen atom of the bridging/structural (occurring on the surface) hydroxyl attached to the octahedral/ tetrahedral metal site present in smectite, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics which are of importance within the framework of HSAB principle. We used "group softness'' for the interacting molecules, whose values were generated by adding the local softness values of constituent atoms of the respective group and found it can be a better descriptor for intermolecular interactions occurring in these NBMs. A semiquantitave scale is proposed from the group reactivity index present in NBM and the clay cluster. (C) 2003 American Institute of Physics.