Which of the following reagents is used for the conversion of $CH_3OH$ to $CH_3COOH$?

Consider the following reactions. From these reactions,which reaction will give carboxylic acid as a major product?
$(A)$ $R-C \equiv N \xrightarrow[(i) H^{+}/H_2O]{\text{mild condition}} R-CONH_2$
$(B)$ $R-MgX \xrightarrow[(ii) H_3O^{+}]{\text{(i) } CO_2} R-COOH$
$(C)$ $R-C \equiv N \xrightarrow[(ii) H_3O^{+}]{\text{(i) } SnCl_2/HCl} R-CHO$
$(D)$ $R-CH_2-OH \xrightarrow{PCC} R-CHO$
$(E)$ $\text{Benzoyl chloride} \xrightarrow[(ii) Br_2/H_2O]{\text{(i) } H_2/Pd-BaSO_4} \text{Benzoic acid}$
Choose the correct answer from the options given below:

How is formic acid prepared?

The major product in the following reaction is:

What is the final product of the following reaction sequence?
$C_4H_8$ $\xrightarrow[\text{peroxide}]{\text{HBr}} X$ $\xrightarrow[\text{(ii) } CO_2]{\text{(i) Mg/dry ether, (iii) } H_3O^+} Y$

$C_6H_5NH_2$ $\xrightarrow{NaNO_2/HCl} X$ $\xrightarrow{Cu_2(CN)_2} Y$ $\xrightarrow{H_2O/H^{+}} Z$
$Z$ is identified as :