$(i)$ Chain isomers of pentane $(C_5H_{12})$:
$1$. $n$-pentane: $CH_3-CH_2-CH_2-CH_2-CH_3$
$2$. Isopentane ($2$-methylbutane): $CH_3-CH(CH_3)-CH_2-CH_3$
$3$. Neopentane ($2,2$-dimethylpropane): $CH_3-C(CH_3)_2-CH_3$
$(ii)$ Isomers of $C_3H_8O$:
$1$. Propan-$1$-ol: $CH_3-CH_2-CH_2-OH$
$2$. Propan-$2$-ol: $CH_3-CH(OH)-CH_3$
$3$. Methoxyethane: $CH_3-O-CH_2-CH_3$
$(iii)$ Isomers of $C_3H_6O$:
$1$. Propanal: $CH_3-CH_2-CHO$
$2$. Propanone: $CH_3-CO-CH_3$
$3$. Allyl alcohol: $CH_2=CH-CH_2OH$
$(iv)$ Metamers in $C_4H_{10}O$ (ethers):
$1$. Methoxypropane: $CH_3-O-CH_2-CH_2-CH_3$
$2$. Ethoxyethane: $CH_3-CH_2-O-CH_2-CH_3$
$3$. $2$-methoxypropane: $CH_3-O-CH(CH_3)_2$