How many molecules are there in 12 grams of ice?

Weigh the ice cube (Let's say it weighs 36 grams, about an ounce)

The weight of 1 mole of water is 18 grams

1 mole of anything contains 6.022 x 1023 molecules

In our example:

36 grams of water contains 36/18=2 moles of water

2 moles of water contains 2x 6.022 x 1023 = 12.044 x 1023 molecules