The gold number of protective colloids A, B, C, and Dare $0.04$, $0.002$, $10$, and $25$ respectively. Which colloid has the highest protective power?

Solution

1. Protective power is defined as being inversely proportional to the gold number.
2. The gold numbers are $0.04$, $0.002$, $10$, and $25$.
3. The smallest gold number indicates the highest protective power.
4. The value $0.002$ is the smallest among the given values.
5. Hence the answer is (B).