The conductivity of 0.001M `Na_2SO_4` solution is `2.6xx10^(-4)Scm^(-1)` and increases to `7.0xx10^(-4)Scm^(-1)`, When the solution is saturated with `CaSO_4`. The molar conductivities of `Na^+` and `Ca^(2+)` are 50 and 120`Scm^2mol^(-1)`, respectively. Neglect conductivity of used water. What is the solubility product fo `CaSO_4`?
A. `4xx10^(-6)`
B. `1.57xx10^(-3)`
C. `4xx10^(-4)`
D. `1.52xx10^(-4) `