A conductivity cell has a cell constant of $0.50\mathrm{c}{\mathrm{m}}^{-1}$. When filled with an electrolyte solution its resistance is $250\Omega$. The conductivity of the solution is

1. A$2.0\times 10^{-3}\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$
2. B$4.0\times 10^{-3}\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$
3. C$125\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$
4. D$5.0\times 10^2\mathrm{S}\mathrm{c}{\mathrm{m}}^{-1}$