Which statement is correct for compounds $A$ and $B$?

$HCN$ and $HNC$ are known as .............

Which of the following are isomers of methyl propanoate?

Which of the following is a pair of functional isomers?

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

The following two compounds are: