In a loss-free R-L-C circuit the transient current is

The correct answer is D. Non-oscillating.

In a loss-free R-L-C circuit, the transient current is non-oscillating. This is because the energy stored in the inductor and capacitor is dissipated in the resistor, causing the current to decay exponentially.

Option A is incorrect because the transient current is not oscillating. Option B is incorrect because the transient current is not a square wave. Option C is incorrect because the transient current is not sinusoidal.