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JEE Main levelSingle correct optionDifficulty 2 of 3sc178

Which order represents decreasing coagulating power of the following electrolytes for a positively charged $Fe (OH) X_{3}$ sol?

A $K X_{2} SO X_{4} > KCl > K X_{3} PO X_{4} > K X_{4} [Fe (CN) X_{6}]$
B $K X_{3} PO X_{4} > K X_{4} [Fe (CN) X_{6}] > K X_{2} SO X_{4} > KCl$
C $KCl > K X_{2} SO X_{4} > K X_{3} PO X_{4} > K X_{4} [Fe (CN) X_{6}]$
D $K X_{4} [Fe (CN) X_{6}] > K X_{3} PO X_{4} > K X_{2} SO X_{4} > KCl$

Answer: D

A positive sol is coagulated by anions, with power increasing with anion charge. The charges are

[Fe (CN) X_{6}] X^{4 -}

(4),

PO X_{4} X^{3 -}

(3),

SO X_{4} X^{2 -}

(2) and

Cl X^{-}

(1). The potassium ion is the same in all four, so the order follows the anion charge.

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