Please solve questions

Dear student
According to the defination : Gold Number is a term used in colloidal chemistry and is defined as the minimum amount of protective colloid in milligrams which change the colour from red to violet of 10 ml gold solution by the addition of 1ml 10 %NaCl solution​​​​​​.

Now according to the given condition

0.025 g of starch needed to prevent coagulation of 1 ml of 10 % NaCl to 10 ml gold sol. 
Amount of starch = 0.025 g = 25 mg
So, gold number of starch = 25

Hence option (4) is correct

Regards
 

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