The number of molecules in a drop of water (0.0018 ml) at room temperature is

Answer

A, B

Explanation

0.0018 ml - drop of water = 0.0018 g H2O = molecular mass = 18 g. Number of molecules in 18 g = `6.023 xx 10^(23)`
Number of molecules in 0.0018 g = `(6.023xx10^(23))/18 xx 0.0018 = 6.023xx10^(23)xx10^(-5)`
`= 6.023xx10^(19)` molecules.
[OR]
Density of water at `25^@` C=997.0479 g/L
Mass of 0.0018 ml (or) `0.0018xx10^(-3)L`
`=DxxV`
`=997.05xx0.0018xx10^(-3)`
`=1.795xx10^(-3)g`
Molar mass of water = 18 g
Mole=`(1.795xx10^(-3))/18=9.971xx10^(-5)` mole
`:.`Number of molecules in 0.0018 ml= moles `xx` Avogadro number
`9.971xx10^(-5)xx6.023xx10^(23)`
`6xx10^(19)` molecules