Explanation

The triple point of water, where ice, liquid water, and water vapour coexist in equilibrium, is at 273.16 K (0.01 degree C) and 611.657 Pa, approximately 611 Pa. Option A gives the wrong pressure, option C the wrong temperature, and option D pairs 373 K with a garbled pressure value. UPSC dropped this question from scoring (marked X in the official key), evidently because of the defective option D, so no candidate was awarded or penalised marks for it. The physically correct values remain those in option B.