Question

Which of the following fluids exhibit(s) non-Newtonian behaviour at 25 °C?

• A. Toothpaste
• B. Mercury
• C. Brine
• D. Blood plasma

Hint:

Non-Newtonian fluids are characterized by a viscosity that changes with the applied shear stress. Examples include shear-thinning fluids like ketchup and toothpaste.

Answer 1

The Correct Option is A, D

Non-Newtonian fluids are those whose viscosity changes under stress or strain. Let us analyze the options:

Step 1: Toothpaste
Toothpaste is a typical example of a non-Newtonian fluid. It behaves as a shear-thinning fluid, meaning its viscosity decreases with increasing shear stress. This makes it a non-Newtonian fluid.
Thus, \( \boxed{A} \) is correct.

Step 2: Mercury
Mercury is a metallic liquid and behaves like a Newtonian fluid. Its viscosity does not change with shear rate, so it does not exhibit non-Newtonian behavior.
Thus, \( \boxed{B} \) is incorrect.

Step 3: Brine
Brine (saltwater) is generally considered a Newtonian fluid under normal conditions. Its viscosity remains constant regardless of the shear rate, so it does not exhibit non-Newtonian behavior.
Thus, \( \boxed{C} \) is incorrect.

Step 4: Blood plasma
Blood plasma is a non-Newtonian fluid. It exhibits shear-thinning behavior, meaning its viscosity decreases under stress. This is due to the complex interactions within the components of blood plasma.
Thus, \( \boxed{D} \) is correct.

Final Answer:
The correct answers are \( \boxed{A}, \boxed{D} \).