Answer
$2.2\times10^{23}\ molecules$
Work Step by Step
Convert grams into moles using the molar mass then multiply by avagadro's number to get the number of molecules.
$6.5g\ H_{2}O\times\frac{1mol\ H_{2}O}{18.015g\ H_{2}O}\times\frac{6.022\times10^{23}\ molecules}{1\ mol}= 2.2\times10^{23}\ molecules$