In an ac circuit, an output capacitor and a resistor are connected in series with an ac signal. What filter action will be the result?

ANS:B - low-pass

From the question, it is clear that the output is taken across the capacitor. So HF signals will get grounded and we will get LF signals in the output. Hence it is LPF.

If the capacitor was connected first and output was taken across the resistor it would be an HPF as the capacitor offer higher impedance to LF signal.

As per my understanding,

Normally with AC signal:

R-C is LPF.
C-R is HPF.

With square wave:

R-C is Integrator.
C-R is a differentiator.