C

Step 1: Analyze the given scenario. We have a loop placed in a magnetic field where the magnetic flux density varies with time.
Step 2: According to Faraday's Law of Electromagnetic Induction, the induced EMF (Electromotive Force) in a closed loop is directly proportional to the rate of change of magnetic flux through the loop. This can be mathematically expressed as:
$$ EMF = -\frac{d\Phi_B}{dt} $$ where $$ \Phi_B $$ is the magnetic flux.
Step 3: Maximum magnetic flux occurs when the magnetic field intensity is at its highest, which would be at t = 4 (this corresponds to option A). Since the induced current is related to the change in magnetic flux, it would be maximum when the rate of change is greatest. This happens right after the maximum flux is reached, at t = 2 (option B), when flux is decreasing at its fastest.
Step 4: The current will be non-zero when there is any change in magnetic flux. Thus, the current will be non-zero at t = 3 (corresponding to option C).
Step 5: The induced current becomes constant when the rate of change of the magnetic flux becomes steady, which would happen at a specific time interval, like t = 5 (option D).
Step 6: Therefore, the correct answer for when the induced current is non-zero is option C (at t = 3).