Maximum efficiency of a reaction turbine The prompt is incomplete and lacks the necessary constraints (e.g., inlet/exit angles, degree of reaction, losses) to state a unique numeric maximum efficiency. Choose the most appropriate statement.

Difficulty: Medium

• η_max = cos²(α) when inlet angle is α and losses are neglected
• η_max occurs at blade speed ratio ρ = cos(α)/2 for a Parsons stage
• 100% (unity), independent of geometry and losses
• Data inadequate — depends on velocity diagrams, reaction, and losses