Total number of isomeric aldehydes and ketones having the molecular formula ${\mathrm{C}}_5{\mathrm{H}}_{10}\mathrm{O}$ are 

7 isomers are possible in which 4 are aldehyde and three are ketones.

Aldehydes:

1.  ${\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2\mathrm{CHO}$ 

$$\begin{gathered} 2. {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{CH}}_2\left({\mathrm{CH}}_3\right)\mathrm{CHO} \\ 3. {\left({\mathrm{CH}}_3\right)}_2{\mathrm{CHCH}}_2\mathrm{CHO} \\ 4. {\left({\mathrm{CH}}_3\right)}_3\mathrm{CCHO} \end{gathered}$$

Ketones:

 $$\begin{gathered} 5. {\mathrm{CH}}_3{\mathrm{COCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3 \\ 6. {\mathrm{CH}}_3\mathrm{COCH}{\left({\mathrm{CH}}_3\right)}_2 \\ 7. {\mathrm{CH}}_3{\mathrm{CH}}_2{\mathrm{COCH}}_2{\mathrm{CH}}_3 \end{gathered}$$