calculate he relative molecular mass of water(H₂O)....?

• Relative molecular mass of a compound can be found by adding the relative atomic mass of the elements present in the compound. It is the mass of a molecules of the compound in comparison to the mass of an atom of C-12 taken as 12.

For H₂O molecule - 

Relative mass of hydrogen (H) = 1u

Relative mass of oxygen (O) = 16u

According to the formula of water contains 2 hydrogen atoms,

So, relative mass of water = 2 *( 1u ) + 16u

= 18u

So, Relative mass of water = 18u