The haemoglobin and the gold sol are examples of:

First, we recall the basic fact about lyophobic colloids: every sol particle acquires an electric charge due to preferential adsorption of ions from the dispersion medium. The sign of this charge depends upon the nature of the substance as well as the ions available in the medium.

We have two colloidal systems mentioned in the question. The first is the sol of haemoglobin. In aqueous medium, haemoglobin molecules preferentially adsorb $$\text{H}^{+}$$ ions (hydrogen ions) from water. Adsorption of positive ions obviously imparts a positive charge to every haemoglobin particle. Hence the haemoglobin sol is a positively charged sol.

Now we examine a gold sol. In water, gold particles preferentially adsorb $$\text{Cl}^{-}$$ ions or other anions that may be present. Adsorption of negative ions gives the gold particles an overall negative charge. Therefore the gold sol is a negatively charged sol.

Summarising the individual results:

$$\text{Haemoglobin sol: positive charge}$$

$$\text{Gold sol: negative charge}$$

So, the pair (haemoglobin sol, gold sol) corresponds to “positively charged” and “negatively charged”, respectively. Looking at the answer options, this description matches Option D, which states “positively and negatively charged sols, respectively.”

Hence, the correct answer is Option D.