Step 1: Recall the three exit conditions for a converging-diverging nozzle.
Let \(p_e\) be the nozzle exit pressure and \(p_a\) the surrounding (ambient/back) pressure.
If \(p_e = p_a\), the jet is ideally expanded and leaves as a straight, parallel stream.
If \(p_e < p_a\) (exit pressure lower than ambient), the jet is overexpanded.
If \(p_e > p_a\) (exit pressure higher than ambient), the jet is underexpanded.
Step 2: Read the wave pattern shown in the figure.
The figure shows the jet boundary curving sharply inward right at the nozzle lip, with oblique waves running from the lip inward to meet on the centerline, then crossing and reflecting outward again, forming the classic repeating shock diamond pattern of a supersonic jet.
Step 3: Match the wave pattern to the physics.
When \(p_e < p_a\) (overexpanded case), the higher outside pressure pushes the jet boundary inward right at the exit. This turning of the flow is achieved through oblique shock waves that start at the nozzle lip and run in towards the centerline, this is exactly the inward-curving, crossing pattern shown in the figure.
If the jet were underexpanded instead (\(p_e>p_a\)), the jet boundary would first bulge outward at the lip (through expansion, or Prandtl-Meyer, fan waves), the opposite of what is drawn.
If the jet were ideally expanded, there would be no waves at all at the exit, and the jet would leave as parallel, wave free flow, but the figure clearly shows a wave pattern.
Step 4: Rule out subsonic flow.
Shock waves and Mach-type wave patterns are a purely supersonic feature, a subsonic nozzle exit flow cannot produce shocks or the crossing-diamond wave pattern shown at all.
Final Answer:
The inward-turning, crossing shock pattern at the exit is the signature of overexpanded flow.
\[ \boxed{\text{Option (A): overexpanded}} \]
