Question

calculate the number of molecules in 90g of water.

Answer 1

To find the number of molecules in 90g of water, first, the number of moles in 90g of water has to be calculated followed by multiplying the moles with 
Avogadro’s number (6.023x10^23). 

 Number of moles can be calculated by the following formula: 

 Number of moles in 90g water= 90/(1+1+16) = 5 

Number of molecules in 90g of water = 5x6.023x10^23

= 30.115x10^23 

Answer 2

I hope it will helpfully to you