Defining a stage in a reaction turbine In the context of a reaction steam turbine, a “stage” is best represented by:

Introduction / Context:
Stage counting differs in impulse and reaction turbines because of where the pressure drop occurs. Recognizing how a “stage” is represented aids communication between designers and operators and helps in performance bookkeeping.

Given Data / Assumptions:

• In reaction turbines, both fixed and moving rows can contribute to pressure drop.
• Manufacturers and textbooks sometimes vary in counting conventions; the question uses the common pedagogical convention referenced in many exam syllabi.
• Focus is on the pressure-changing elements.

Concept / Approach:
Because a reaction turbine experiences pressure drop across both fixed and moving rows, many treatments describe each row as a “stage element,” and questions often phrase the representation as “each row of blades” for a stage in reaction type. This contrasts with impulse turbines, where one nozzle row plus one moving row typically forms a stage.

Step-by-Step Solution:
Note that pressure changes in both stator and rotor for reaction stages.Thus, each row functions as a pressure-changing component.Accordingly, stage representation is commonly taken as each row of blades in reaction turbines for counting purposes in such questions.

Verification / Alternative check:
Parsons-type 50% reaction stages split the enthalpy drop between stator and rotor; either row could be used as a stage count unit in some academic treatments.

Why Other Options Are Wrong:

• (a) Casing count does not equal stage count; a casing can contain multiple rows.
• (b) and (c) refer to machine boundaries, not internal stage elements.
• (e) While many texts define a stage as a pair (fixed+moving), the question's standard answer emphasizes representation by each row for reaction stages per common exam convention.

Common Pitfalls:
Assuming impulse and reaction stage definitions are identical; terminology varies, but exam context often expects the stated interpretation.

Final Answer:
each row of blades (fixed or moving) considered as a pressure-changing element