Question

calculate the number of molecules in 90 g of water

Answer 1

Molar mass of water = 18 g mol^​-1
18 g of water contains = 6.022$\times$10²³ of molecules
90 g of water contains = $\frac{6.022\times {10}^{23}}{18}\times 90$ = 30.11$\times$10²³ molecules