Answer:

you need the molar mass of water

an oxygen atom wieghs 16 atomic units

(au) and the two hydrgen atoms in water wiegh two au the molar mass of water is therefore 18 au

this means that 1 mole of waters wieghs 18 grams

1 mole＝18 grams

xmoles＝6.5 grams

therefore x = (6.5×1)/18＝0.361 moles

1mole contains 6.022141 × 10 20 particles

we have 0.61 moles so

0.361 x 6.022141 x 10 23 = 2.174 x 10 23 molecules.

Explanation:

hope it helps