The molar conductivities at infinite dilution of barium chloride, sulphuric acid and hydrochloric acid are \( 280 \), \( 860 \) and \( 426 \; \mathrm{S \, cm^{2} \, mol^{-1}} \) respectively. The molar conductivity at infinite dilution of barium sulphate is ______ \( \mathrm{S \, cm^{2} \, mol^{-1}} \).
