An optically active amino acid (A) can exist in three forms depending on the pH of the medium. If the molecular

formula of (A) is C3H7NO2 write
(i) structure of compound (A) in aqueous medium. What are such ions called?
(ii) In which medium will the cationic form of compound (A) exist?
(iii) In alkaline medium, towards which electrode will the compound (A) migrate in electric field?

To answer these questions, we need to understand the behavior of an optically active amino acid (A) in different pH mediums. Let's break down the questions one by one.

(i) Structure of compound (A) in aqueous medium:
An amino acid consists of a carboxyl group (-COOH), an amino group (-NH2), and a side chain (R) attached to a central carbon atom. In the given molecular formula C3H7NO2, there are three carbon atoms, seven hydrogen atoms, one nitrogen atom, and two oxygen atoms.

In an aqueous medium, an amino acid (A) exists in its ionized form, which means it undergoes ionization by losing or gaining protons (H+). The carboxyl group (-COOH) can lose a proton to form a negatively charged carboxylate ion (-COO-). The amino group (-NH2) can gain a proton to form a positively charged ammonium ion (-NH3+).

Therefore, the structure of the compound (A) in aqueous medium will have a negatively charged carboxylate group (-COO-) and a positively charged ammonium group (-NH3+). The side chain (R) remains unchanged.

(ii) In which medium will the cationic form of compound (A) exist?
The cationic form of compound (A) refers to the positively charged form of the amino acid. In this case, it is the ammonium ion (-NH3+). This form exists in an acidic medium, where there is an excess of H+ ions. In such a medium, the amino group can readily accept a proton to form the cationic form.

(iii) In alkaline medium, towards which electrode will the compound (A) migrate in an electric field?
In an electric field, when a compound migrates towards a specific electrode, it depends on the charge on the compound. Since in an alkaline medium, the compound (A) will exist in its ionized form, which means it will have a negatively charged carboxylate group (-COO-).

Negatively charged ions are attracted to the positively charged electrode (anode) in an electric field. Therefore, the compound (A) will migrate towards the anode in an alkaline medium.

In summary:
(i) The structure of compound (A) in aqueous medium will have a negatively charged carboxylate group (-COO-) and a positively charged ammonium group (-NH3+).
(ii) The cationic form of compound (A) will exist in an acidic medium.
(iii) In an alkaline medium, compound (A) will migrate towards the anode in an electric field.