Number of water molecules in a drop of water, if `1 mL` of water has 20 drops and `A` is Avogadro's number, is

Options

A. `0.05A`
B. `0.5 A`
C. `(0.05A)/(18)`
D. `(0.5 A)/(18)`

Answer

C

Explanation

Number of `H_(2)O` molecules in one drop
`(("Mass of one drop" H_(2)O)/("Molar mass of" H_(2)O))` (Avogadro's constant)
Mass of 1 drop `H_(2) O` = (Volume of one drop `H_(2)O`) `xx` (Density)
`= (1//20 mL) (1g mL^(-1)) = 1//20g`
`:.` Number of `H_(2)O` molecules `= (1//20g)/(18g mol^(-1)) xx A = (0.05A)/(18)`