(1)

Metamerism occurs when the compound has different number of carbon atoms on either side of the functional group. Metamers of $C_4{H}_{10}O$:

$\begin{array}{c}{\mathrm{CH}}_3-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3\\ \mathrm{Methylpropyl} \mathrm{ether}\\ {\mathrm{CH}}_3{\mathrm{CH}}_2-\mathrm{O}-{\mathrm{CH}}_2{\mathrm{CH}}_3\\ \mathrm{Diethyl} \mathrm{ether}\end{array}$

(1)

$\mathrm{\alpha }$-Hydrogen at bridge carbon never participate in tautomerism. Thus, only (III) exhibits tautomerism.

[IMAGE 60]

(2)

[IMAGE 62]

(3)

Enolic form of ethyl acetoacetate has 18 $\mathrm{\sigma }$-bonds and 2$\mathrm{\pi }$-bonds