Which of the following compounds are isomers of propionic acid?

Among the following,identify the compound that is not an isomer of hexane $(C_6H_{14})$:

Dimethyl ether and ethyl alcohol are

Identify the pairs of compounds which are functional group isomers.
$I$. $CH_3-CH_2-CH_2-CH_2-OH$
$II$. $CH_3-CH_2-CH(OH)-CH_3$
$III$. $(CH_3)_3C-OH$
$IV$. $CH_3-CH(CH_3)-CH_2-OH$
$V$. $CH_3-CH_2-O-CH_2-CH_3$
$VI$. $CH_3-O-CH_2-CH_2-CH_3$
$VII$. $CH_3-O-CH(CH_3)_2$

Among the following,the most stable compound is:

How many asymmetric carbons are present in the following molecule? $HOCH_2-CH(Br)-CH(Br)-CH_2OH$