The potential difference between the fixed and mobile part of double layer in soil colloids is known as

Correct option is D

The correct answer is (D) Zeta potential

Explanation:
• Soil colloids (clay and humus) possess a negative surface charge. In a soil solution, they attract a layer of counter-ions (cations).
• This creates an "Electric Double Layer" consisting of a Stern layer (fixed ions tightly bound to the surface) and a Diffuse layer (mobile ions in the solution).
• The Zeta potential is the electrokinetic potential at the slipping plane (the boundary where the mobile part of the solution starts moving relative to the particle surface).
• It is a measure of the magnitude of the electrostatic or charge repulsion/attraction between particles and is one of the fundamental parameters known to affect stability (flocculation vs. dispersion).

Information Booster:
• A high zeta potential (positive or negative) indicates that the particles will repel each other, leading to a dispersed (stable) suspension.
• A low zeta potential (near zero) means the repulsive forces are weak, and particles will clump together (flocculate).
• The point at which the zeta potential is zero is called the Isoelectric Point.

Additional Knowledge:
• Total water potential (Option A): The sum of various forces (matric, osmotic, gravitational) acting on soil water.
• Gravitational potential (Option C): Potential energy of water due to its elevation in the Earth's gravitational field.
• Theta potential (Option B): Likely a distractor, though "Theta" is often used to represent volumetric water content in soil physics.