The correct figure that shows, schematically, the wave pattern produced by the superposition of two waves of frequencies 9 Hz and 11 Hz, is

When two waves of slightly different frequencies $$f_1 = 9$$ Hz and $$f_2 = 11$$ Hz are superimposed, the phenomenon of beats is produced.

The resultant displacement can be written as $$y = y_1 + y_2 = 2A\cos\left(\frac{\omega_1 - \omega_2}{2}t\right)\sin\left(\frac{\omega_1 + \omega_2}{2}t\right)$$.

The term $$2A\cos\left(\frac{\omega_1 - \omega_2}{2}t\right)$$ acts as the slowly varying amplitude envelope, and $$\sin\left(\frac{\omega_1 + \omega_2}{2}t\right)$$ is the rapidly oscillating carrier wave at frequency $$\frac{f_1 + f_2}{2} = 10$$ Hz.

The beat frequency is $$f_{\text{beat}} = |f_1 - f_2| = |9 - 11| = 2$$ Hz. This means the amplitude envelope completes 2 full cycles per second, so the listener hears 2 beats per second.

The correct schematic figure must show a rapidly oscillating wave at 10 Hz whose amplitude is modulated by an envelope that rises and falls 2 times every second. Over a 1-second interval, there should be 2 distinct regions of maximum loudness (constructive interference) and 2 regions of near-zero amplitude (destructive interference).

Among the given figures, the one showing this amplitude modulation pattern with 2 beats per second is the correct answer, which is Option A.