The volume of a drop of water is 0.0018 mL then the number of water molecules present in two drop of water at room temperature is:

Mass of a drop of water = 0.0018g
Moles of water  $=\frac{0.0018}{18}={10}^{-4}\mathrm{mole}$
Number of water molecules in one drop  = 10^-4  N_A
Number of water molecules in two drops $= 2\times {10}^{-4}\times 6.023\times {10}^{23}=12.046\times {10}^{19}$