Identify compound $A$ in the following reaction.
$R-Mg-X + A$ $\xrightarrow{\text{dry ether}} R-COOMgX$ $\xrightarrow[\text{dil } HCl]{H_2O} R-COOH + Mg(X)OH$

What is $A$ in the following reaction?
$Cyclopropyl bromide \xrightarrow[(ii) CO_2, (iii) H_3O^+]{(i) Mg, Et_2O} A$

$Ph-C(=O)-CH_3$ $\xrightarrow[HCl]{NaNO_2} (A)$ $\xrightarrow[heat]{Ac_2O} (B)$ $\xrightarrow{H_3O^{+}} (C)$
Product $(C)$ of the above reaction is

Find product $V$ in the following reaction sequence:
$CH_3-CH(CH_3)-COOH$ $\xrightarrow[H_3O^{+}]{LiAlH_4} I$ $\xrightarrow{PBr_3} II$ $\xrightarrow[ether]{Mg} III$ $\xrightarrow{CO_2} IV$ $\xrightarrow{H_3O^{+}} V$

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

What is obtained when glycerol is heated with oxalic acid at $110\,^{\circ}C$?