What is the number of structural isomers of $C_3H_6O$?

The compound with the molecular formula $C_3H_6O$ can show:

The number of possible structural isomers for the molecular formula $C_3H_5Cl$ is ...............

The number of metamers possible for $C_{4}H_{10}O$ is

Identify the pairs of compounds that represent position isomerism:
$(I)$ $CH_3-CH_2-CH_2-CH_2-OH$
$(II)$ $CH_3-CH_2-CH(OH)-CH_3$
$(III)$ $CH_3-C(CH_3)(OH)-CH_3$
$(IV)$ $CH_3-CH(CH_3)-CH_2-OH$
$(V)$ $CH_3-CH_2-O-CH_2-CH_3$
$(VI)$ $CH_3-O-CH_2-CH_2-CH_3$
$(VII)$ $CH_3-O-CH(CH_3)-CH_3$

Metamerism can be exhibited by the compounds containing