What is the molecular mass of water? 

Explanation

Molecules mass=Real mass of one molecules
`6.022xx10^(23)` water molecules=18g
`"One water molecules" = ("Gram Mol. Wt.")/("Av. Number")`
Mass of a molecules `=(18)/(6.022)xx10^(23)=2.99xx10^(-23)`g
Molecular mass of water is `2.99xx10^(-26)` kg