Write the reaction showing `alpha`-halogenation of carboxylic acid and give its name .

Explanation

Carboxylic acids having `alpha`-hydrogen are halogenated at the `alpha` position on treatment with chlorine or bromine in presence of small amount of red phosphorous to give `alpha`-halo carbonxylic acids.
This reaction is named as Hell-volhard -Zelinsky (HvZ) reactions.
`{:(R-CH_(2)-COOH underset("ii)" H_(2)O)overset("i)" x_(2)//"Red"'p')to R-underset(X)underset(|)(CH)-COOH),(" "X-Cl"," Br),(" "alpha-"Halo Carboxylic acid"):}`