mole concept ques

Question

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

Answer 1

Density of water = 1 g/ml
mass of 0.0018 ml of water = 0.0018×1 = 0.0018 g
molar mass of water = 18 g/mol
number of moles in 0.0018g of water = 0.0018/18 = 10^-4 moles

number of water molecules in 1 mole = 6.022×10²³ molecules
number of water molecules in 10^-4 mole = 10^-4*6.022*10²³ = 6.022*10¹⁹ molecules

So, the number of water molecules present in two drop of water = 2* 6.022*10¹⁹

= 12.04*10¹⁹

So the correct option is (A)