Using Darcy's Law,
\[
Q=KiA
\]
Substituting the given values,
\[
Q=(2\times10^{-4})(0.02)(0.5)
\]
\[
Q=2\times10^{-6}\ \mathrm{m^3/s}
\]
Hence,
\[
\boxed{Q=2\times10^{-6}\ \mathrm{m^3/s}}
\]
Therefore, the correct answer is
\[
\boxed{(A)}
\]
Note: Although the image marks option (B) as correct, applying Darcy's Law with the given values yields \(2\times10^{-6}\ \mathrm{m^3/s}\). Thus, the marked key appears to contain an error.