So, the correct order is order is $\mathrm{F}>\mathrm{Ce}>\mathrm{Br}$
$F C H_{2} C O O H>C l C H_{2} C O O H>B r C H_{2} C O O H>C H_{3} C O O H$
$C{{H}_{3}}-C{{H}_{2}}-COOH\xrightarrow{PC{{l}_{3}}}I\xrightarrow{{{C}_{6}}{{H}_{6}}/AlC{{l}_{3}}}II\xrightarrow[\text{base/heat}]{N{{H}_{2}}-N{{H}_{2}}}III$