`10^(-4)` g of gelatin is required to be added to 100 `cm^(3)` of a standard gold sol to just prevent its coagulation by the addition of 1 `cm^(3)` of 10% NaCl solution to it. Hence, the gold number of gelatin is

Options

A. 10
B. 1
C. 0.1
D. 0.01

Answer

D

Explanation

By definition, gold number is the number of milligrams of dry protective colloids required to just prevent the coagulation of 10mL of red gold sol when 1 mL (or 1 `cm^(3)` ) of 10% NaCl solution is added to it.
Here the amount of gelatin required to protect 10 mL (or 10 `cm^(3)`) of gold sol
`=(10^(-4)xx10)/(100)=10^(-5) g`
`=10^(-5)xx10^(-3) mg=10^(-2)` mg
=0.01 mg
`therefore` Gold number =0.01