(i) In Hell-Volhard-Zelinsky (HVZ) reaction, carboxylic acid having an $\mathit{\alpha }$-hydrogen is halogenated at $\mathit{\alpha }$-position on treatment with chlorine or bromine in the presence of red phosphorus to give $\mathit{\alpha }$-halogenated carboxylic acid.

(ii) In decarboxylation reaction, carboxylic acid loses ${\mathrm{CO}}_2$ to form hydrocarbons when their sodium salts are heated with sodalime $(\mathrm{NaOH}$ and $\mathrm{CaO}$ ) in the ratio $3:1$.