Pls ! i’m not very smart so explain it to me!

3.01  x 10²¹

Explanation:

Molar mass of h₂o =18.01528 g/mol.

it means 1 mole h₂o=18.01528 g (1)

1 mole = 6.022 × 10^23 molecules

so,

1 mole  h₂o =6.022 × 10^23 molecules=18.01528 g  [from 01]

now,

18.01528 g h₂o has= 6.022 × 10^23 molecules

9.00x10⁻² g h₂o has= ( 6.022 × 10^23 x 9.00x10⁻² ) /18.01528 molecules

                                  =3.008 x 10²¹ molecules

                                  ≈ 3.01  x 10²¹ molecules