JEE Main levelNumerical answerDifficulty 2 of 3sc189
Gold number is the mass of protective colloid, in mg, that just prevents coagulation of 10 mL of a gold sol on adding 1 mL of 10% NaCl. If 2.7 mg of a protein just protects 60 mL of the same gold sol, find its gold number (two decimals).
Numerical answer type, answer in mg, tolerance 0.01.
Answer: 0.45 mg
Mass needed per 10 mL of sol =2.7×10/60=0.45mg. This is the gold number.