Step 1: Write the formula
Molar conductivity links to specific conductance by \(\Lambda_m=\frac{\kappa\times1000}{M}\), where \(M\) is the molarity and the factor 1000 converts cm\(^3\) to litres.
Step 2: Substitute
\[ \Lambda_m=\frac{2.50\times10^{-4}\times1000}{0.0020}=\frac{0.25}{0.0020}=125\text{ S cm}^2\text{ mol}^{-1} \]
Step 3: Check the options
\(62.5\) comes from using \(0.004\) M, \(12.5\) from dropping a factor of 10, and \(250\) from using \(0.001\) M. The correct value is \(125\), option (A).
Final Answer:
\(\Lambda_m=125\) S cm\(^2\) mol\(^{-1}\), option (A).
\[ \boxed{\text{(A) } 125} \]