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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3sc153

The gold numbers (in mg per 10 mL of a standard gold sol) are gelatin 0.01, gum arabic 0.15 and starch 25. Select the correct statements.

AGum arabic is a better protective colloid than gelatin
B $0.30 mg$ of gum arabic can protect $20 mL$ of the standard gold sol
CStarch is 2500 times less effective than gelatin on a mass basis
D $1.0 mg$ of gelatin can protect only $100 mL$ of the standard gold sol

Answer: B, C

A smaller gold number means better protection, so gelatin beats gum arabic.

0.30

mg of gum arabic protects

(0.30/0.15) \times 10 = 20

mL, so that statement is correct. Starch to gelatin is

25/0.01 = 2500

, which is correct.

1.0

mg of gelatin protects

(1.0/0.01) \times 10 = 1000

mL, not 100 mL.

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