In this question we have given the gram of water and we know that 1 mole of water = 18 gram of water and 27 g of water contain 1.5 g of water 27 / 18 = 1.5 g
As we know that avogandro'S no is equal 6.022*1023
1.5g * 6.022*1023 = 9.0 * 1023 molecules present in each 27 g of water.
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