Answer:
the unknown substance is a protein
Explanation:
The biuret test is one of the tests for proteins. It can be used to detect peptide linkages. The biuret test is carried out in an alkaline solution. A coordination complex is formed leading to the appearance of a violet color.
Summarily, the biuret method is a colorimetric technique used to test for proteins and peptides. It involves the formation of a purple (violet) complex of Copper salts in alkaline solution.
Hence when the biuret reagent is added to an unknown substance and it turns purple, the unknown substance is a protein
Mass of reactants > mass of products
Physical properties are those which can be observed without any change in composition of the substance. Hence, a is the answer.
1. Mg + CuSO4 —> MgSO4 + Cu
=> Single displacement reaction
2. 2HCI + Mg(OH)2 —> MgCI2 + H2O
=> Acid - base reaction
3.AgNO3 + NaCI —> AgCI + NaNO3
=> Double displacement reaction
