Answer
The order of acidity is :
$CH_3CHBrCH_2CH_2COOH \lt CH_3CH_2CHBrCH_2COOH \lt CH_3CH_2CH_3CHBrCOOH$
Work Step by Step
We know, the stronger acid has a more stable conjugate base. In these compounds, Br is an electron withdrawing substituent. The closer the electron withdrawing substituent is to the COOH group, the more stable is the carboxylate ion, and the acid is stronger. So, The order of acidity is :
$CH_3CHBrCH_2CH_2COOH \lt CH_3CH_2CHBrCH_2COOH \lt CH_3CH_2CH_3CHBrCOOH$
