Which reaction is used for the preparation of $\alpha$-bromoacetic acid?

$X \xrightarrow{PCl_5} C_2 H_5 Cl$
$Y \xrightarrow{PCl_5} CH_3 COCl$
$X$ and $Y$ are:

The compound $(X)$ in the given reaction is:
$MeO-C_6H_4-CHO + (X) \xrightarrow{CH_3COONa, H_3O^+} MeO-C_6H_4-CH=CHCOOH$

In the reaction,if $X$ is the reagent and $Y$ is the product,which of the following is not feasible?

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

Which of the following acids remains unaffected on heating?