How can $A$ and $B$ be differentiated?

$3-\text{Hydroxybutanal}$ is formed when $X$ reacts with $Y$ in dilute $Z$ solution. What are $X, Y$ and $Z$? $(X, Y, Z)$

In the following reaction:
$HC \equiv CH \xrightarrow[{Hg^{2+}}]{{H_2SO_4}} 'P'$
Product $'P'$ will not give:

$\text{Phthalic anhydride}$ $\xrightarrow {PCl_5} A$ $\xrightarrow {LiAlH_4} B$ $\xrightarrow {PCC} C$ $\xrightarrow [\Delta ] {OH^{-}} D$
Compound $D$ is :-

How will you convert butan-$2$-one to propanoic acid?
$CH_3-CH_2-CO-CH_3 + I_2 + NaOH$ $\rightarrow C_2H_5CO_2^-Na^+ + CHI_3$ $\xrightarrow{H^+} C_2H_5COOH$

Identify the product formed in the following reaction: $CH_3-CH=CH-CH_2-CHO \xrightarrow[(ii) \ H_3O^{+}]{(i) \ LiAlH_4} \text{Product}$