We present our calculations based on density functional theory to explore the molecular adsorption of O-2 on the first-row transition-metal dicarbides C2X (X = Sc-Zn). Degree of activation of O-2 is observed to be less in C2XO2 (X = Sc-V) as compared with C2XO2 (X = Cr-Zn) except for X = Cu, and is marked by the amount of total charge on O-2. Topological analysis shows that the interaction in the cases of C2XO2 (X = Sc-V) is prominent between X and O and mostly being intermediate type whereas in C2XO2 (X = Cr-Zn), both C-O and X-O bondings are observed with shared-kind and intermediate characteristics respectively. (C) 2015 Elsevier B.V. All rights reserved.