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On addition of one mL solution of 10% Na...

On addition of one mL solution of 10% NaCl to 10 ml. gold sol in presence of 0.0025 g of starch, the coagulation is just prevented. The gold number of starch is

A

`25`

B

`0.025`

C

`0.25`

D

`2.5`

Text Solution

Verified by Experts

The correct Answer is:
A
Gold number of protective colloid is :
"Colloid in milligrams which when added to 10 mL of gold solution just prevents its coagulation by 1 mL of 10% NaCl solution" .
Protective power `prop (1)/("gold number")`
The gold number of starch is 25, because it has very low protective power.
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