Find the number of molecules in 27 grams of water

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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since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.