The vitamin riboflavin, which occurs as a yellow pigment in egg yolk and milk become

• colorless on reduction with Zn in acid and regained its color on re-oxidation
• colorless on oxidation and regained its color on reduction with Zn in acid
• more deep in color on reduction with Zn in acid and regained its color on re-oxidation
• more deep in color on oxidation and regained its color on reduction with Zn in acid