Which of the following is most acidic?

The descending order of acidity among the following compounds is:

$2,2-$ Dimethylpropanoic acid on heating with sodalime gives:

Propanoic acid undergoes the $HVZ$ reaction to give $2-$chloropropanoic acid. The product obtained is:

Arrange the products $I$,$II$,$III$ from the following reactions in decreasing order of their acid strength.
$A) \text{Propylbenzene} \xrightarrow[\text{ (ii) } H_3O^{+}]{\text{ (i) } KMnO_4 / OH^{-}} I$
$B) CH_3COOH \xrightarrow[\text{ (ii) } H_2O]{\text{ (i) } Br_2 / \text{red } P} II$
$C) \text{Bromobenzene}$ $\xrightarrow[\substack{\text{ (ii) } CO_2 / \text{dry ether} \\ \text{ (iii) } H_3O^{+}}]{\text{ (i) } Mg / \text{dry ether}} III$

The decreasing order of nucleophilicity among the following nucleophiles is:
$(I)$ $CH_3-COO^{-}$
$(II)$ $CH_3O^{-}$
$(III)$ $C_6H_5O^{-}$
$(IV)$ $CH_3-SO_3^-$