Carboxylic acids having an a-hydrogen are halogenated at the α-position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give α-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.

What happens when α-Bromopropionic acid undergo substitution reaction with ammonia?

α-Aminopropionic acid 

The correct answer is option 2. α-Aminopropionic acid.

When α-Bromopropionic acid undergoes a substitution reaction with ammonia (NH₃), it forms α-Aminopropionic acid, also known as Alanine.

The product formed is α-Aminopropionic acid, also known as Alanine (\( \text{CH}_3\text{CH}_2\text{NH}_2\text{COOH} \)). Ammonia replaces the bromine atom in α-Bromopropionic acid, resulting in the formation of an amino group (-NH₂) in the α position to the carboxyl group. When α-Bromopropionic acid undergoes a substitution reaction with ammonia, it forms α-Aminopropionic acid, also known as Alanine. Therefore, the correct answer is α-Aminopropionic acid.