Acetone reacts with iodine (I₂) to form iodoform in the presence of

$\begin{array}{r}{\mathrm{CH}}_3{\mathrm{COCH}}_3+3{\mathrm{I}}_2+4\mathrm{NaOH}⟶\\ \text{ Acetone }\end{array}$

$$\begin{gathered} {\mathrm{CHI}}_3+3\mathrm{NaI}+{\mathrm{CH}}_3\mathrm{COONa}+3{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Iodoform} \end{gathered}$$

Thus acetone reacts with iodine to form iodoform in the presence of NaOH.