Q42. For a strong electrolyte, a plot of molar conductivity against (concentration) ${ } ^ { 1 / 2 }$ is a straight line, with a negative slope, the correct unit for the slope is\\
(1) $\mathrm { Scm } ^ { 2 } \mathrm {~mol} ^ { - 3 / 2 } \mathrm {~L} ^ { - 1 / 2 }$\\
(2) $\mathrm { Scm } ^ { 2 } \mathrm {~mol} ^ { - 3 / 2 } \mathrm {~L} ^ { 1 / 2 }$\\
(3) $\mathrm { Scm } ^ { 2 } \mathrm {~mol} ^ { - 3 / 2 } \mathrm {~L}$\\
(4) $\mathrm { Scm } ^ { 2 } \mathrm {~mol} ^ { - 1 } \mathrm {~L} ^ { 1 / 2 }$