The negatively charged sol among the following is:

The correct answer is option 4. \(Sb_2S_3\, \ sol\).

The negatively charged sol can be determined by considering the nature of the colloidal particles and their charge. Let's analyze the given options:

1. \(Fe(OH)_3\, \text{sol}\): Iron(III) hydroxide, \(Fe(OH)_3\), is a positively charged sol. The hydroxide ions (\(OH^-\)) in the colloidal particles have a negative charge, but the overall colloid is positively charged.

2. Haemoglobin: Haemoglobin is a protein and generally carries a net negative charge in solution.

3. \(TiO_2\, \text{sol}\): Titanium dioxide, \(TiO_2\), is a metal oxide. The surface of \(TiO_2\) sol particles can carry a negative charge, making the sol negatively charged.

4. \(Sb_2S_3\, \text{sol}\): Antimony(III) sulfide, \(Sb_2S_3\), is a negatively charged sol. The sulfide ions (\(S^{2-}\)) in the colloidal particles have a negative charge, contributing to the overall negative charge of the sol.

Therefore, the negatively charged sol among the given options is 4. \(Sb_2S_3\, \text{sol}\).