Which of the following statements regarding thermodynamic processes and the Second Law is/are TRUE?

(A) The entropy of an isolated system never decreases during any spontaneous process

(B) A perpetual motion machine of the second kind (PMM-2) violates the Kelvin-Planck statement

(C) The efficiency of all reversible engines operating between the same two thermal reservoirs is identical

(D) During an irreversible adiabatic process, the entropy of the system remains strictly constant

Answer Key:

A,B,C

### 5-Stage Derivation & Analytical Solution: 1. **Stage 1: Governing Concept & Domain Context:** * This question evaluates **Brayton Cycle with Real Component Efficiencies** under *Thermodynamic Cycles of Gas Turbines* in GATE AE. 2. **Stage 2: Mathematical Derivation:** * Statements A, B, and C reflect the fundamental tenets of the Second Law of Thermodynamics and Carnot's theorem. Statement D is false because entropy is conserved only in reversible adiabatic (isentropic) processes; for irreversible adiabatic processes, entropy increases due to internal entropy generation ($S_{gen} > 0$). 3. **Stage 3: Distractor Elimination Forensics:** * The evaluated correct answer is derived using standard physical equations. * Distractor values correspond to typical unit conversion omissions or inverted formulas. 4. **Stage 4: Common Student Trap:** * *Trap:* Assuming all adiabatic processes are isentropic. *Reference: Philip G. Hill, Carl R. Peterson, Mechanics and Thermodynamics of Propulsion (Pearson).*

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