Natural abundance of heavy water in water is `1: 6000`. How many heavy water molecules are present in one drop of water ? (one mL water is 20 drops)

Explanation

One mL water =one gram (d=1 g per mL)
weight of one drop of water `=(1)/(20)g`
weight of `D_(2)O` in one drop of water `=(1)/(20 xx 6000)g`
Number of moles of `D_(2)O =("weight")/(GMW)=(1)/(20 xx 6000 xx 20)`
Number of `D_(2)O` molecules =Number of moles `xx N_(A)`
`=(6.022 xx 10^(23))/(20 xx 6000 xx 20)=2.51 xx 10^(17)`
Number of heavy water molecules is `2.51 xx 10^(17)`