**Question:** Gibbs-Donnan effect is seen on the distribution of:

A. Electrolytes
B. Water
C. Oxygen
D. Nitrogen gases

**Core Concept:** The Gibbs-Donnan effect is a phenomenon that influences the distribution of electrolytes across semi-permeable membranes. It is based on the unequal distribution of ions caused by the presence of charged molecules or ions in the solution on both sides of the membrane.

**Why the Correct Answer is Right:** The Gibbs-Donnan effect affects the distribution of electrolytes, specifically sodium (Na+) and potassium (K+), based on the concentration gradient and the presence of charged molecules or ions on either side of the semi-permeable membrane. In this case, the correct answer is A: Electrolytes.

**Why Each Wrong Option is Incorrect:**

B. Water: The Gibbs-Donnan effect primarily influences the distribution of electrolytes, not water. Water moves along the osmotic gradient, while the Gibbs-Donnan effect deals with the distribution of charged particles.

C. Oxygen: The Gibbs-Donnan effect is specific to electrolytes and does not involve the distribution of gases such as oxygen.

D. Nitrogen gases: Similar to option C, the Gibbs-Donnan effect is specific to electrolytes, not gases.

**Clinical Pearl / High-Yield Fact:** The Gibbs-Donnan effect is important in understanding the distribution of electrolytes in various physiological and pathological conditions, such as osmotic diuresis and oedema. It highlights the role of charged molecules and ions in determining the distribution of substances across membranes, and has implications for clinical practice, particularly in managing fluid and electrolyte imbalances.

**Correct Answer:** A. Electrolytes