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 is treated with alcoholic KOH?

Acrylic acid 

The correct answer is option 2. Acrylic acid.

When α-Bromopropionic acid is treated with alcoholic KOH, a dehydrohalogenation reaction occurs. This reaction involves the elimination of HBr, resulting in the formation of a double bond. The product of this reaction is acrylic acid.

The alcoholic KOH (potassium hydroxide in alcohol) provides a strong base (alkoxide ion, RO⁻).The alkoxide ion abstracts a proton (H⁺) from the β-carbon (the carbon adjacent to the carbon bearing the bromine atom), leading to the formation of a double bond and the elimination of HBr. When α-Bromopropionic acid is treated with alcoholic KOH, the product formed is acrylic acid. Therefore, the correct answer is Acrylic acid.