First, we calculate the number of moles of urea in the solution. Number of moles of urea ($n$) = $\frac{\text{Given number of molecules}}{\text{Avogadro's number } (N_A)}$ $n = \frac{6.02 \times 10^{20}}{6.02 \times 10^{23}} = 10^{-3} \text{ mol} = 0.001 \text{ mol}$

Next, we calculate the concentration (molarity) of the solution. Molarity ($M$) is defined as the number of moles of solute dissolved in one litre of solution . $\text{Volume of solution} = 100 \text{ mL} = 0.1 \text{ L}$ $M = \frac{\text{Moles of solute}}{\text{Volume of solution in litres}} = \frac{0.001 \text{ mol}}{0.1 \text{ L}} = 0.01 \text{ M}$.