This behaviour is best understood by comparing a compressor blade to an aircraft wing. A wing generates lift smoothly only as long as the air flows attached to its curved upper surface; if the angle at which air meets the wing (the angle of attack) becomes too large, the airflow separates from the surface and lift collapses, which pilots know as a stall. Compressor blades work on exactly the same aerodynamic principle. When the mass flow through the compressor drops or the operating condition moves away from the design point, the angle at which air strikes the rotor blades increases beyond the safe limit, the boundary layer peels off the blade surface, and the air stream simply stops following the curved blade contour. This local breakdown of flow over the blade is called stalling. It is different from surging, which is a violent, whole-machine flow reversal, and from choking, which happens when the flow reaches sonic speed at the narrowest section. Since the question specifically describes the air failing to follow the blade shape, the answer is stalling, option (C).