The minimum number of amide isomers possible for ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{ON}$ 

${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{ON}$, chemically also known as propanamide is a mono-substituted amide.  Propanamide exhibits structural isomerism and the minimum number of amide isomers possible for it is 4. The isomers are shown below. 

Hence, 4 numbers of amide isomers are possible for ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{ON}$. 

Therefore, option (A) is correct.