The number of water molecules is maximum in

$18grams$ of water corresponds to $1mole$ and contains $= 6 .02 \times {10}^{23}$water molecules.
$18moles$ of water contains$= 18 \times 6 .02 \times {10}^{23}$ water molecules.
$18$ molecules of water
$1 . 8grams$ of water contain $\dfrac{1 . 8}{18} \times {N}_{A} = 0 . 1{N}_{A}$ water molecules.

So, $18mole$ water has a maximum number of molecules.