JEE Main · 2021 · 24 Feb 2021 · Shift 2 · Surface Chemistry

Blood is a negatively charged sol, so it is coagulated by the positive ion of any electrolyte added to it. By the Hardy-Schulze rule the coagulating power of that ion rises steeply with its charge, since a more highly charged cation neutralises the negative charge on the colloidal particles far more effectively. Of the salts listed only $\mathrm{FeC}{\mathrm{l}}_3$ supplies a trivalent cation, $\mathrm{F}{\mathrm{e}}^{3+}$, against the divalent and monovalent cations of the others, so $\mathrm{FeC}{\mathrm{l}}_3$ is the most efficient salt for clotting blood.