If the density of some lake water is `1.25 g mL^(-1)` and contains `92g` of `Na^(o+)` ions per `kg` of water, calculate the molality of `Na^(o+)` ions in the lake.

Explanation

`"No. of moles in 92 g of Na"^(+) " ions "=("92 g")/("23 g mol"^(-1))="4 moles (as atomic mass of NA = 23)"`
As these are present in 1 kg of water, by definition, molality = 4m.