1g of ordinary water corresponds to $\frac{1}{6000}$​g of heavy water.
Thus, 0.01g of ordinary water corresponds to $\frac{1\times {10}^{-5}}{6}$​ g of heavy water.

$$\begin{gathered} \mathrm{Moles} \mathrm{of} \mathrm{heavy} \mathrm{water} =\frac{\mathrm{Weight} \mathrm{of} \mathrm{heavywater}}{\mathrm{Molar} \mathrm{mass} \mathrm{of} \mathrm{heavywater}}=\frac{{10}^{-5}}{6\times 20}=\frac{{10}^{-6}}{12} \\ \mathrm{No}. \mathrm{of} \mathrm{molecules} = \frac{6.023\times {10}^{23}}{12} \times {10}^{-6}\approx 5\times {10}^{16} \end{gathered}$$