Which aldehyde is used to preserve biological specimens?

$\mathrm{P} \stackrel{{\mathrm{H}}_2/\mathrm{Pd}-{\mathrm{BaSO}}_4}{\to } \mathrm{Q} \underset{\left(\mathrm{ii}\right) \mathrm{dil}. \mathrm{HCl}}{\overset{\left(\mathrm{i}\right) \mathrm{conc}. \mathrm{NaOH}}{\to }} \mathrm{R}+\mathrm{S}$

$\mathrm{R}$ and $\mathrm{S}$ form benzyl benzoate when treated with each other. Hence, $\mathrm{P}$ is

What is Formalin? Write its use.

Which of the following compounds is used in the preservation of biological specimens?

The major product of the following reaction is:

$\mathrm{Assertion} :-$ Ethyl acctoacetate forms butane- $1,4$ -diol with ${\mathrm{NaBH}}_4$.

$\mathrm{Reason} :-$ ${\mathrm{NaBH}}_4$ can reduces ketone and esters group.