Maximum Induced EMF in Square Loop in Time Varying Magnetic Field

The magnetic flux through the square loop is given by $\Phi = B A \cos\theta$.

According to Faraday's law of electromagnetic induction, the magnitude of the induced electromotive force (emf) is $e = \left|\frac{d\Phi}{dt}\right|$.

Differentiating the magnetic flux with respect to time gives the maximum induced emf as $e_{\text{max}} = B_0 A \omega \cos\theta$.

Substituting the given values $B_0 = 0.4\text{ T}$, $A = 4 \times 10^{-4}\text{ m}^2$, $\omega = 300\text{ rad/s}$, and $\theta = 60^\circ$ yields $e_{\text{max}} = 24\text{ mV}$.

Therefore, the correct option is D.