Gold numbers of protective colloids \(\mathrm{A}, \mathrm{B}, \mathrm{C}\) and \(\mathrm{D}\) are \(0.50,0.01,0.10\) and \(0.005\), respectively. The correct order of their protective powers is: (a) \(\mathrm{D}<\mathrm{A}<\mathrm{C}<\mathrm{B}\) (b) \(\mathrm{C}<\mathrm{B}<\mathrm{D}<\mathrm{A}\) (c) \(\mathrm{A}<\mathrm{C}<\mathrm{B}<\mathrm{D}\) (d) \(\mathrm{B}<\mathrm{D}<\mathrm{A}<\mathrm{C}\)

In the field of chemistry, particularly when dealing with colloidal systems, the term 'protective colloid' refers to a substance that, when added in small quantities, stabilizes colloids against coagulation. Coagulation is a process where particles in a colloid aggregate to form larger clusters, eventually causing the system to separate into two phases.

Protective colloids work by forming a thin layer around the dispersed particles, which offers steric stabilization. This prevents the particles from coming too close together, thereby averting coagulation. A common example is the addition of gelatin to gold sols, where the gelatin adsorbs onto the surface of the gold particles.

The effectiveness of a protective colloid is assessed by its gold number. The lower the gold number, the more effective the colloid is at providing protection to the system. The utility of protective colloids is seen in a wide range of industries including food, pharmaceuticals, and photography.

The prevention of coagulation is essential in maintaining the stability and functionality of a colloidal system. Protective colloids achieve this by several mechanisms, including electrostatic repulsion and steric hindrance.

Electrostatic repulsion involves the charge on the particles. Protective colloids can add like charges to the surface of colloidal particles, causing them to repel one another, thus reducing the likelihood of coagulation. Meanwhile, steric hindrance occurs when the large molecules of the protective colloid create a physical barrier that prevents the particles from coming into direct contact.

Both mechanisms are crucial as they assure that colloidal particles remain sufficiently separated. The fundamental importance of this prevention is evident in everyday products like paints and inks, where uncontrolled coagulation can lead to poor performance or spoilage of the product.

Colloid protective power is essentially a measure of how well a protective colloid can prevent coagulation in a colloidal system. The higher the protective power, the more stable the colloid, even with the addition of electrolytes or other agents that may prompt coagulation.

The protective power of a colloid is quantified using the 'gold number'. This number is determined by adding the protective colloid to a standard gold sol and then introducing an electrolyte that causes coagulation. The gold number is the minimum amount of protective colloid that is required to prevent the coagulation of a fixed amount of gold sol after the addition of the electrolyte.

A higher protective power corresponds to a smaller gold number, signifying that less colloid is needed to stabilize the system. This inherent protective power is invaluable not only in industrial applications but also in biological systems, where enzymes and other proteins must be kept stable in a colloidal state within bodily fluids.