Final answer:
Gelofusine is not a crystalloid because it is a colloid, containing larger molecules that do not dissolve but instead create a suspension to act as a plasma substitute. Option B is correct.
Step-by-step explanation:
The answer to the question of which substance is not a crystalloid is B. gelofusine. Crystalloid solutions are aqueous solutions of mineral salts or other water-soluble molecules. Hartmann's solution and dextrose solutions (C. dextrose solution and D. dextrose 10%) are examples of crystalloid solutions because they contain electrolytes and/or sugars that can readily dissolve in water, forming a true solution.
Gelofusine, on the other hand, is a colloid solution because it contains larger insoluble molecules designed to mimic the osmotic pressure of blood. It is often used as a plasma substitute for patients.