How many of the isomeric ketones having the molecular formula ${\mathrm{C}}_6{\mathrm{H}}_{12}\mathrm{O}$ undergo iodoform test 

Four isomeric ketones i.e.,  

$$\begin{gathered} {\mathrm{CH}}_3{\mathrm{COCH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_2{\mathrm{CH}}_3, \\ {\mathrm{CH}}_3\mathrm{COCH}\left({\mathrm{CH}}_3\right){\mathrm{CH}}_2{\mathrm{CH}}_3 \\ {\mathrm{CH}}_3{\mathrm{COCH}}_2\mathrm{CH}{\left({\mathrm{CH}}_3\right)}_2 \\ \text{and }{\mathrm{CH}}_3\mathrm{COC}{\left({\mathrm{CH}}_3\right)}_3 \end{gathered}$$ 

undergo iodoform test.