Correct choice is (a) 18Cr-8Ni in H2SO4
To explain I would say: Stainless steel (18Cr–8Ni) in sulfuric acid will corrode exponentially with the increase in temperature. Whereas stainless steel in nitric acid, nickel in sodium hydroxide, monel for hydrofluoric acid are the best corrosion-resistant materials in respective mediums and suffer less corrosion with the increase in temperature.