Question

In addition of $1mL$ solution of $10\% $ NaCl to $10mL$ gold sol in the presence of $0.0250g$ of starch, the coagulation is just prevented. Starch has the gold number.
 A.$0.025$
 B.$0.25$
 C.$2.5$
 D.$25$

Answer 1

Hint: We have to know that starch or amylum is a polymeric sugar composed of various glucose units joined by glycosidic bonds. The polysaccharide is created by the most green plants for energy stockpiling. It is the most well-known starch in human weight control plans and is contained in huge sums in staple food sources like potatoes, corn, rice, wheat and cassava.

Complete answer:
We have to know that, the Gold Number is the base weight (in milligrams) of a defensive colloid needed to forestall the coagulation of $10mL$ of a standard hydro gold sol when 1 ml of a $10\% $ sodium chloride arrangement is added to it. It was first utilized by Richard Adolf Zsigmondy. An electrical twofold layer is ordinarily present on the gold sol particles, bringing about electrostatic repugnance between the particles. The sodium chloride particles upset this electrical twofold layer, making coagulation happen.
The coagulation of gold sol brings about an increment in molecule size, demonstrated by a shading change from red to blue or purple. The higher the gold number, the lower the defensive force of the colloid, in light of the fact that a more noteworthy measure of colloid is needed to forestall coagulation.
In the given details, the measure of starch is added to $10mL$ of gold sol, which is needed to forestall coagulation of $1mL$ of $10\% $ NaCl = $0.0250g$ = $25mg$ . At the point when the starch is needed to be added to $10mL$ to gold sol totally. Forestall coagulation by 1mL of $10\% $ NaCl arrangement.
Therefore,
$ = \dfrac{{25}}{{100}} \times 10 = 2.5mg$
The gold number of starch is $2.5$ .

Hence, the correct option is (C) $2.5$ .

Note:
Being awesome transmitters of warmth and power, the metal does not get influenced via air and most reagents. The component is consumption safe, and is available in stores of alluvium and veins. Most basic gold mixtures incorporate chloroauric corrosive and auric chloride. To give more solidarity to the metal, another delicate metal is alloyed to it.