In colloidal solution of blue ink following reagent are mixed
`H_2O`, Egg,` CH_3COOH` & HCl
then which of the obove reagent ensure the stability of blue ink

Options

A. `H_2O`
B. Egg albumen
C. `CH_3COOH`
D. HCl

Answer

To determine which reagent ensures the stability of blue ink in a colloidal solution, we need to analyze the role of each reagent when mixed with the blue ink.

### Step-by-Step Solution:

1. **Understanding the Components**:
- Blue ink is a colloidal solution, where the dispersed phase (blue dye) is suspended in the dispersion medium (water).
- The reagents to be mixed are water (H₂O), egg (which contains proteins), acetic acid (CH₃COOH), and hydrochloric acid (HCl).

2. **Role of Water (H₂O)**:
- Water is the dispersion medium in which the blue ink is already suspended. Adding more water will dilute the solution but will not significantly affect the stability of the colloidal particles.

3. **Role of Egg**:
- Egg contains proteins, which can interact with the colloidal particles. Proteins can carry a negative charge and may lead to coagulation if they adsorb onto the positively charged dye particles in the blue ink. This would destabilize the colloidal solution.

4. **Role of Acetic Acid (CH₃COOH)**:
- Acetic acid is a weak acid that can dissociate to form acetate ions. These ions can interact with the colloidal particles but do not significantly contribute to the stability of the colloid.

5. **Role of Hydrochloric Acid (HCl)**:
- HCl is a strong acid that completely dissociates in solution, providing a high concentration of hydrogen ions (H⁺). The presence of H⁺ ions can help maintain the charge balance in the colloidal solution, which can enhance the stability of the colloidal particles by preventing coagulation.

6. **Conclusion**:
- Among the reagents mixed, **HCl** is the one that ensures the stability of the blue ink colloidal solution. It helps maintain the charge balance and prevents coagulation of the colloidal particles.

### Final Answer:
**HCl ensures the stability of blue ink in the colloidal solution.**