A student uses the Biuret test on four solutions and records colour changes. Which result correctly indicates the presence of protein?

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Question

A student uses the Biuret test on four solutions and records colour changes. Which result correctly indicates the presence of protein?

Accepted Answer

The solution turns purple after adding Biuret reagent — The Biuret reagent produces a purple (violet) colour in the presence of protein, because peptide bonds react with copper ions in alkaline conditions. Remaining blue indicates no protein is detected. An orange-red result is associated with Benedict's reagent detecting a reducing sugar, not protein. A blue-black colour is produced when iodine solution reacts with starch, not protein.

Answer

The solution turns purple after adding Biuret reagent

Answer

The solution turns orange-red after adding Biuret reagent

Answer

The solution remains blue after adding Biuret reagent

Answer

The solution turns blue-black after adding Biuret reagent

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