Hi Heena, we need more details about what exactly you want to measure. If you want to see how quanity of H2O2 and NO changes after treatment with antioxidant I would suggest using these kits, I've used them myself and in my opinion they work well
We also multiplex those kits with this one in order to measure number of living cells https://www.promega.com/products/cell-health-assays/cell-viability-and-cytotoxicity-assays/celltiter_glo-2_0-assay/ for normalization purpose
follow this article as she performed 9 different antioxidant activities including the one you mentioned. very useful article https://linkinghub.elsevier.com/retrieve/pii/S0308814610004188