Select the correct statement for 50% reaction stage in a steam turbine.

The correct answer is: The absolute exit flow angle is equal to inlet angle of rotor blade.

Explanation:
In a steam turbine, the degree of reaction (R) is defined as the ratio of the static enthalpy drop in the rotor to the total static enthalpy drop in the stage (stator + rotor). For a 50% reaction stage, also known as a Parson's reaction turbine, the enthalpy drop is equally shared between the fixed blades (stator) and the moving blades (rotor). This symmetric distribution of enthalpy drop leads to symmetric velocity triangles for the stage.

For symmetric velocity triangles in a 50% reaction stage, the following relationships hold between the absolute and relative flow angles at the inlet (subscript 1) and outlet (subscript 2) of the rotor:

$${\alpha }_1={\beta }_2$$

and

$${\alpha }_2={\beta }_1$$

Where:
- ${\alpha }_1$ is the absolute inlet flow angle (angle of the fluid leaving the stator and entering the rotor).
- ${\beta }_1$ is the relative inlet flow angle (which is equal to the inlet angle of the rotor blade for shockless entry).
- ${\alpha }_2$ is the absolute exit flow angle of the fluid leaving the rotor.
- ${\beta }_2$ is the relative exit flow angle (which is equal to the outlet angle of the rotor blade).

From the relation ${\alpha }_2={\beta }_1$, we can clearly see that the absolute exit flow angle (${\alpha }_2$) is equal to the inlet angle of the rotor blade (${\beta }_1$). This confirms the correctness of the statement.