(i) In Hell-Volhard-Zelinsky (HVZ) reaction, carboxylic acid having an α-hydrogen is halogenated at α-position on treatment with chlorine or bromine in the presence of red phosphorus to give α-halogenated carboxylic acid.
RCH2‌COOH‌

‌ (i) ‌X2∕Red‌P

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(ii)H2O

‌

RCHCOOH |

X

(ii) In decarboxylation reaction, carboxylic acid loses CO2 to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaO ) in the ratio 3:1.
RCOONa‌

NaOH‌ and ‌CaO

─────▸

∆

‌RH+Na2CO3