The substance a thus added to stabilize the emulsions are called emulsifiers or emulsifying agents. Emulsion of oil in water(o/w):- the emulsion in which oil is the dispersed phase and water is the dispersion medium. 

Emulsions are a type of mixture that consists of two immiscible liquids, such as oil and water. They are created by dispersing one liquid phase (called the dispersed phase) into another liquid phase (called the continuous phase) with the help of an emulsifying agent. The emulsifying agent plays a crucial role in stabilizing the emulsion by reducing the interfacial tension between the two phases and preventing them from separating.

The correct answer to the given question is option 'C', which states that the substances added to stabilize emulsions are called emulsifying agents. Emulsifying agents are also known as emulsifiers or surfactants. They have both hydrophilic (water-loving) and hydrophobic (oil-loving) properties, which allow them to interact with both the dispersed and continuous phases of the emulsion.

Emulsifying agents work by forming a protective layer around the dispersed droplets, preventing them from coalescing and causing the emulsion to break. This layer reduces the interfacial tension between the two phases and provides stability to the emulsion. Emulsifying agents can be classified into two types:

1. Natural Emulsifiers: These are substances that are naturally present in certain foods or can be derived from natural sources. Examples of natural emulsifiers include egg yolk, mustard, and lecithin.

2. Synthetic Emulsifiers: These are artificially produced emulsifiers that are commonly used in the food and cosmetic industries. Synthetic emulsifiers have specific properties that make them suitable for stabilizing emulsions. Examples of synthetic emulsifiers include polysorbates, sorbitan esters, and sodium stearoyl lactylate.

Emulsifying agents can be added to emulsions during their preparation or can be incorporated into pre-made products to enhance their stability. They are typically used in various food products, such as mayonnaise, salad dressings, and ice cream, as well as in cosmetic and pharmaceutical formulations.

In conclusion, emulsifying agents are substances added to stabilize emulsions by reducing the interfacial tension between the dispersed and continuous phases. They form a protective layer around the dispersed droplets, preventing them from coalescing and maintaining the stability of the emulsion.