The enol form of acetone after reacting with ${\mathrm{D}}_2\mathrm{O}$ gives

The enol form of acetone on treatment with ${\mathrm{D}}_2\mathrm{O}$ undergoes enolisation, deutration (addition of ${\mathrm{D}}_2\mathrm{O}$ ) and dehydration (removal of ${\mathrm{H}}_2\mathrm{O}$ ). The repeated enolisation, deutration and dehydration ultimately gives ${\mathrm{CD}}_3{\mathrm{COCD}}_3$.

Hence the correct answer is (B)