A sample of red ink (a colloidal suspension) is prepared by mixing eosine dye, egg white, HCHO and water. The component which ensures stability of the ink sample is:

In the preparation of red ink, the mixture obtained is a colloidal system. For any colloidal sol to remain stable, the dispersed particles must not aggregate and settle. Stabilisation is usually achieved by adding a suitable substance called a protective colloid, which gets adsorbed on the surface of the dispersed particles and prevents them from coming together.

We have four components in the recipe:

(i) Eosin dye – this gives the red colour and forms the dispersed phase.
(ii) Water – this acts as the dispersion medium in which the dye particles remain suspended.
(iii) HCHO (formaldehyde) – this serves mainly as a preservative to prevent microbial growth and has no significant role in colloid protection.
(iv) Egg white – this is largely a protein (albumin). Proteins are excellent protective colloids because their long-chain molecules adsorb firmly on the surface of dye particles, producing a sheath that repels other particles through solvation and charge effects.

Because of this adsorbed protein layer, the dye particles do not aggregate, and the sol remains stable for a long time. None of the other ingredients provides such a stabilising sheath.

Hence, the component that ensures the stability of the ink sample is the egg white.

Hence, the correct answer is Option A.