Select the most appropriate option about boiling and condensation processes as expressed by the statements P, Q and R.
P – The quantities of heat involved in evaporation and condensation of unit mass of fluid are identical
Q – The boiling and condensation of a single compound normally occur isothermally
R – The condensation is achieved at or below dew point and boiling occurs at triple point
Options:
(A) All P, Q and R are true
(B) Only P and Q are true
(C) Only P is true
(D) Only Q is true
Official Answer Key:
B
Step-by-Step Solution & Explanation
P is true: for a pure substance, the latent heat released on condensation equals the latent heat absorbed on evaporation of the same mass (they are the same physical property, hg−hf, traversed in opposite directions). Q is true: for a single (pure) compound at constant pressure, both boiling and condensation occur at a fixed saturation temperature, i.e. isothermally. R is false: condensation occurs at or below the dew point, but boiling occurs at the saturation temperature corresponding to the operating pressure — not specifically at the triple point (a fixed, unique point, not a general boiling condition). Answer: (B).
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