Question

Which of the following statements are true
A. Water solubility of an amino acid is maximum at a pH when concentrations of anions and cations are equal.
B. Amino acids can be detected by ninhydrin test
C. On reacting with nitrous acid amino acids release $N_2$

• A. All
• B. B and C
• C. A and B
• D. only A

Answer 1

The correct option is B B and C

Amino acids can form zwitter ions, that is a molecule or ion having separate positively and negatively charged groups. Amino acids form due to the presence of an amine group, that can ionize to form ${NH}_3^{+}$ and a carboxyl group that can form ${COO}^{-}$. When they are in the zwitter ion form, they do not migrate in an electric field and they precipitate out of the solution. Therefore amino acids are least soluble at a pH when they exist in the zwitter ion form, that is when the concentration of anions and cations are equal.
The other two statements are true:
The amine group of amino acids reacts with ninhydrin reagent to give a purple colour complex.
And amino acids react with nitrous acid releasing $N_2$.