The coagulation of `100mL` of a colloidal solution of gold is completely prevented by adding `0.25g` of starch to it before adding `10mL` of `10%NaCl` solution. The gold number of starch is

Answer

B

Explanation

[10 ml of `10%` NaCI solution is added to 100 ml of solution of gold.
thus, 1 ml of 10% NaCI solution has been added to 10 ml solution of gold.
Since, 100 ml gold solution required `=0.25g` starch
`=0.25xx10^(3)` mg starch
so, 10 ml gold solution required `=(0.25xx10^(3))/(100)xx10`
Thus, by definition, the gold number of starch is `25`.]