JEE Main · 2020 · 07 Jan 2020 · Shift 2 · Redox Reactions and Electrochemistry

By Kohlrausch's law each ion makes a fixed contribution to the molar conductivity, so any valid equation must leave the same ionic difference on both sides. The relation that fails sets $({\Lambda }_m^0{)}_{\mathrm{NaBr}}-({\Lambda }_m^0{)}_{\mathrm{NaI}}$, which is really ${\Lambda }_{{\mathrm{Br}}^{-}}^0-{\Lambda }_{{\mathrm{I}}^{-}}^0$, equal to $({\Lambda }_m^0{)}_{\mathrm{KBr}}-({\Lambda }_m^0{)}_{\mathrm{NaBr}}$, which is ${\Lambda }_{{\mathrm{K}}^{+}}^0-{\Lambda }_{{\mathrm{Na}}^{+}}^0$ — an anion difference matched against a cation difference. Those are unrelated quantities, so that is the incorrect equation, while the others do balance like differences on both sides.