Consider the following statements about amino acids:

A. Nitrous acid liberates nitrous oxide from amino acids

B. An important sensitive test for the detection of amino acids is the ninhydrin colour test

C. Glycine is the only amino acid that does not possess a chiral centre.

D. All the natural amino acids that occur as constituents of proteins belong to the L-series

Which of these statements are correct?

B, C and D

The correct answer is option 3. (B), (C) and (D).

Statement A: Nitrous acid liberates nitrous oxide from amino acids

The statement is incorrect. Nitrous acid \((HNO_2)\) does not liberate nitrous oxide \((N_2O)\) from amino acids. Nitrous acid is a weak acid that can dissociate in water to produce hydrogen ions \((H^+)\) and nitrite ions \((NO_2^-)\). It is not involved in the direct liberation of nitrous oxide from amino acids. Nitrous oxide, also known as laughing gas, is a different compound with the chemical formula \(N_2O\). It is commonly used as an anesthetic and has various industrial applications. However, the liberation of nitrous oxide from amino acids does not occur through a direct reaction with nitrous acid. The breakdown of amino acids can occur through different processes such as decarboxylation, deamination, or transamination, depending on the specific amino acid and the conditions present. These processes may result in the formation of various byproducts, but nitrous oxide is not a typical byproduct of amino acid breakdown.

Statement B: An important sensitive test for the detection of amino acids is the ninhydrin colour test

This statement is correct.  The ninhydrin color test is indeed an essential and sensitive method for detecting the presence of amino acids. It works by reacting with primary amines, such as the amino groups \((-NH_2)\) present in amino acids, to form colored products. The reaction with ninhydrin results in the formation of a purple or blue-colored complex, known as Ruhemann's purple. This color change is highly sensitive and can detect even small amounts of amino acids.

The ninhydrin color test is widely used in biochemical and analytical laboratories for qualitative and quantitative analysis of amino acids, as well as in other fields such as forensic science for detecting fingerprints. Therefore, it is an important and sensitive test for the detection of amino acids.

Statement C: Glycine is the only amino acid that does not possess a chiral centre.

This statement is correct. Glycine is the only amino acid that does not possess a chiral center. This is because glycine has a single carbon atom with two hydrogen atoms and an amino group attached to it. This carbon atom does not have any asymmetric carbon atoms, so it does not have a chiral center.

A chiral center is an atom that has four different groups attached to it. This means that the atom can exist in two different forms, which are mirror images of each other. These mirror images are called enantiomers.

The vast majority of amino acids have at least one chiral center. This is because the carbon atom that is attached to the amino group and the carboxyl group is asymmetric. However, glycine does not have this asymmetric carbon atom, so it does not have a chiral center.

The lack of a chiral center in glycine has some implications for its chemical properties. For example, glycine is optically inactive, which means that it does not rotate the plane of polarized light.

Statement D: All the natural amino acids that occur as constituents of proteins belong to the L-series

This statement is correct. In nature, all the amino acids that serve as building blocks for proteins are of the L-configuration, also known as the "L-series." This refers to the orientation of the amino group \((-NH_2)\) and the carboxyl group \((-COOH)\) around the central carbon atom. In the L-configuration, the amino group is on the left side when the molecule is drawn in a Fischer projection, hence the designation "L."

The L-configuration is prevalent in proteins found in living organisms, while the D-configuration (where the amino group is on the right side) is less common and typically found in certain bacterial cell walls and a few other specialized contexts.