Step 1: Conductivity and Solubility Product.
The conductivity \( \kappa \) of a saturated solution of AgCl can be related to its solubility product \( K_{sp} \). The solubility product \( K_{sp} \) is given by:
\[
K_{sp} = s^2
\]
where \( s \) is the solubility of AgCl. Using the conductivity, we can calculate \( s \) and thus \( K_{sp} \).
Step 2: Conclusion.
The correct answer is (C), \( 4.0 \times 10^{-8} \, \text{M}^2 \).