Of the given options, sugar C₁₂ H₂₂ O₁₁ is the most soluble in water H₂ O, followed by common salt NaCl, camphor C₁₀ H₁₆ O, and sulphur S₈ in that order. Water H₂ O is called a universal solvent because it dissolves the majority of compounds present in the earth’s crust. Sugar C₁₂ H₂₂ O₁₁ is a polar molecule that readily dissolves in water due to the water molecule’s ability to form hydrogen bonds with the polar sugar molecule, making it highly soluble. Common salt NaCl is also a polar molecule, but its solubility is slightly lower than that of sugar C₁₂ H₂₂ O₁₁. Camphor C₁₀ H₁₆ O is a nonpolar molecule and has low solubility in water H₂ O. Sulphur S₈ is also a nonpolar molecule and is only slightly soluble in water H₂ O.

Therefore, the answer is c. Sugar.