Question

On heating, the colour of zinc oxide changes from white to yellow. This is a/an:

• A. physical change
• B. chemical change
• C. photochemical change
• D. irreversible change

Answer 1

Answer: (B)

chemical change

Zinc oxide is a white powder, when heated strongly (above ${800}^{0}C$) it turns yellow, but again becomes white again when cold. The hot zinc oxide absorbs some of the blue wavelengths of light making the reflected light more yellow. The loss of oxygen makes it a reversible chemical change.