Final answer:
The hair will change color when testing for metallic salts, such as when copper wire in silver salt solution turns blue due to Cu²⁺ releasing. This color change or precipitate formation helps identify specific metallic salts.
Step-by-step explanation:
When performing a test to determine whether metallic salts are present, the hair will change color in the solution if metallic salts are present. For instance, when placing copper wire in a solution containing a dissolved silver salt, silver ions are reduced to elemental silver on the surface of the copper wire, and the Cu²⁺ ions dissolve in the solution to yield a characteristic blue color. This is similar to a qualitative analysis in which chloride ions are added to a test solution, causing the formation of a precipitate if certain metallic ions like Ag⁺, Pb²⁺, or Hg2²⁺ are present. When a pale yellow precipitate forms after adding silver nitrate solution to a test solution, it indicates the presence of a particular salt. These tests help in identifying the presence of metallic salts through color changes or the formation of precipitates.