An engine operating between the boiling and freezing points of water will have
A. Efficiency more than 27%.
B. Efficiency less than the efficiency of a Carnot engine operating between the same two temperatures.
C. Efficiency equal to 27%.
D. Efficiency less than 27%.
Choose the correct answer from the options given below

The absolute temperatures for the boiling point ($$T_H$$) and freezing point ($$T_C$$) of water are:

$$T_H = 100^\circ\text{C} = 373\text{ K}$$

$$T_C = 0^\circ\text{C} = 273\text{ K}$$

Maximum limiting Carnot efficiency:   $$\eta_{\text{Carnot}} = 1 - \frac{273}{373} = \frac{100}{373} \approx 0.268 \text{ or } 26.8\%$$

Since any actual operating engine has an efficiency strictly lower than the Carnot limit ($$\eta < 26.8\%$$), its efficiency is automatically less than $$27\%$$.