Question

Which of the following protective colloids has high gold number:

• A. Acacia
• B. Tragacanth
• C. Albumin
• D. Gelatin

Answer 1

The Correct Option is B

The correct option is (B): Tragacanth.

Answer 2

The gold number tells us how good a protective colloid is at stopping a gold sol from flocculating (turning color/coagulating) when salt is added. A lower gold number means the colloid protects well with only a small amount, while a higher gold number means a much larger amount is needed, so the colloid is a weaker protector. Let's rank the four options.

1. Acacia: Acacia (gum arabic) has a fairly low gold number, roughly in the range of 0.1 to 0.2 mg, showing it protects a gold sol quite efficiently at small doses.
2. Tragacanth: Tragacanth has a gold number of about 2, which is many times higher than acacia, albumin, or gelatin. This means a much larger quantity of tragacanth is needed to give the gold sol the same protection, so it is the weakest protective colloid of the group.
3. Albumin: Egg albumin has a low gold number, around 0.1, close to acacia, meaning it protects strongly at small amounts.
4. Gelatin: Gelatin has one of the lowest gold numbers of any common colloid, around 0.005 to 0.01, making it the strongest protective colloid among the four.

Since a high gold number signals weak protective power, and tragacanth's gold number is far above that of acacia, albumin, and gelatin, tragacanth is the one with the highest gold number here.

So the correct answer is Tragacanth.