Hey there!
First let's convert grams to moles.
There are 18.02 grams in every mole, so divide 175.2 by 18.02.
175.2 ÷ 18.02 = 9.723
We have 9.723 moles of water.
There are 6.022 x 10²³ molecules in each mole, so multiply that by 9.723.
9.723 x 6.022 x 10²³
58.55 x 10²³
5.855 x 10²⁴
There are 5.855 x 10²⁴ molecules of water in 175.2 grams of water.
Hope this helps!