Explanation:



Zwitterions are dipolar ions in which the positive and negative charges are separated in such a way that they are located in different parts of the molecule. The term "zwitterion" comes from the German word "zwitter," which means "hermaphrodite" or "hybrid."

Glycine is the only compound among the given options which exists as a zwitterion. The reason for this is that glycine has both an acidic carboxyl group (-COOH) and a basic amino group (-NH2) in the same molecule. The carboxyl group can donate a proton (H+) to the amino group, resulting in the formation of a zwitterion.

Structure of glycine:




Formation of zwitterion:




In the acidic medium, glycine exists as a cationic form (H3N+CH2COOH), whereas in the basic medium, it exists as an anionic form (H2NCH2COO-). However, in the physiological pH (around 7.4), both the amino and carboxyl groups are partially ionized, resulting in the formation of a zwitterion (H3N+CH2COO-).

Advantages of zwitterions:


Zwitterions have several advantages over other compounds, which make them useful in various applications. Some of these advantages are:

- Zwitterions are highly soluble in water due to their dipolar nature, which makes them useful in the pharmaceutical industry for drug delivery.
- Zwitterions are less likely to interact with other molecules, which makes them useful in the production of chromatographic columns for separating biomolecules.
- Zwitterions have a high affinity for metal ions, making them useful in the production of metal-organic frameworks (MOFs) for gas storage and separation.

Conclusion:


Thus, glycine is a typical example of a compound that exists as a zwitterion due to the presence of both an acidic carboxyl group and a basic amino group in the same molecule.