Which of the following has the highest flocculating power?

$[Fe(CN)_6]^{4-}$

The correct answer is option 1. \([Fe(CN)_6]^{4-}\).

The flocculating power of an electrolyte is determined by its ability to neutralize the charges on colloidal particles, leading to their aggregation or coagulation. In the case of a positively charged sol, such as a positive sol, adding an electrolyte with a high flocculating power results in the neutralization of the positive charges on the colloidal particles. This neutralization reduces the electrostatic repulsion between the particles, allowing them to come closer together and eventually form aggregates or precipitates.

The ion \([Fe(CN)_6]^{4-}\) is highly negatively charged (\(-4\)) and relatively large due to the presence of multiple cyanide ligands. This high charge and larger size enhance its ability to neutralize the positive charges on the colloidal particles effectively. As a result, colloidal particles in a positive sol treated with \([Fe(CN)_6]^{4-}\) experience significant electrostatic neutralization, leading to rapid coagulation and precipitation.

In contrast, ions with lower charges or smaller sizes may have less flocculating power because they are less effective at neutralizing the charges on colloidal particles.

Therefore, \([Fe(CN)_6]^{4-}\) is the correct choice for the electrolyte with the highest flocculating power for a positive sol.