When two drops of copper sulphate and 10 drops of caustic soda are added to a food containing protein the colour changes to?

1. (A), (B), (D), (C)
2. ​(B), (A), (D), (C)
3. ​(B), (A), (C), (D)
4. ​(D), (B), (A), (C)

Hide Solution(s)

When two drops of copper sulphate and ten drops of caustic soda or NaOH is added to egg, it turns violet. This indicates the presence of proteins.This is Biuret's test and the principle is simple as follows:

In the presence of alkaline medium (caustic soda or NaOH), the Cu2+ ions get reduced to Cu+ and binds to the egg proteins, thereby giving a violet color.

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Video showing Test for Presence of Protein in Food

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When copper sulphate and caustic soda are added to a food sample, a violet color indicates the presence of proteins in the food.