Which of the following substance/s will precipitate the emulsion which is negatively charged?

A. \(KCl\)

2. \(Glucose\)

3. \(NaCl\)

4. \(Urea\)

Choose the correct anwer from the options given below:

A, C only

The correct answer is option 3. A, C only. 

Let us look at a detailed explanation considering the potential charge-neutralizing effects of \(KCl\) and \(NaCl\) on negatively charged emulsion particles.

Emulsions typically consist of dispersed droplets in a continuous phase. The stability of emulsions is influenced by the surface charge on the droplets. If the emulsion particles carry a negative charge, they may experience electrostatic repulsion, preventing the droplets from coalescing and leading to emulsion stability.

The addition of certain salts can influence the stability of the emulsion by screening the charges on the droplets. Specifically, salts that dissociate into ions in solution can contribute to charge neutralization. Let's consider the case of \(KCl\) and \(NaCl\):

1. \(KCl\):
When dissolved in water, \(KCl\) dissociates into \(K^+\) and \(Cl^-\) ions. The chloride ions (\(Cl^-\)) can interact with the negatively charged emulsion particles, potentially neutralizing their charges to some extent.

2. \(NaCl\):
Similarly, \(NaCl\) dissociates into \(Na^+\) and \(Cl^-\) ions in solution. The chloride ions (\(Cl^-\)) can also interact with the negatively charged emulsion particles, contributing to charge neutralization.

While these salts may not completely neutralize the charges, they can screen the repulsive forces between the negatively charged emulsion particles, leading to reduced electrostatic repulsion. This reduction in repulsion can promote the coalescence of emulsion droplets and eventually lead to the precipitation or breaking of the emulsion.

In summary, the addition of \(KCl\) and \(NaCl\) can impact the stability of a negatively charged emulsion through charge screening effects, leading to potential precipitation. Therefore, Option 3. A, C only is a valid choice in this context.