Correct option is C
Surging is a type of unstable operation in centrifugal compressors and sometimes axial compressors.
It occurs when the compressor operates at low mass flow rates, near the left-hand side of its performance curve.
At these low flows:
The pressure ratio demanded by the system is higher than the compressor can stably deliver.
Flow in the diffuser and impeller passages reverses periodically.
This causes large oscillations in flow and pressure → loud noise, vibration, and possible mechanical damage.
