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 = 0.0018gMoles of water  =0.001818=10−4moleNumber of water molecules in one drop  = 10-4  NANumber of water molecules in two drops = 2×10−4×6.023×1023=12.046×1019