The weight of water containing 6 × 10¹⁰ atoms of oxygen is

One mol of oxygen atoms = 6.023 × 10²³ atoms are present in 18 grams of H₂O.

$\text{ Weight of water containing }6\times {10}^{10}\text{ atoms of ' O ' }=\frac{6\times {10}^{10}\times 18}{6.023\times {10}^{23}}=1.79\times {10}^{-12}\mathbf{g}$