The law of constant proportion states that a sample of pure water will always form Y%Y% mass of OO and X%X% mass of HH irrespective of its source. Find YY.

The law of constant proportions, also known as the law of definite proportions, states that a chemical compound will always contain the same proportion of elements by mass. For water (H2O), this means that the proportion of hydrogen (H) and oxygen (O) will always be the same, regardless of the source of the water.

Water is composed of 2 hydrogen atoms and 1 oxygen atom. The atomic mass of hydrogen (H) is approximately 1 gram/mole, and the atomic mass of oxygen (O) is approximately 16 grams/mole.

So, in one molecule of water:

• The total mass contributed by Hydrogen (H) is: 2 * 1 = 2 grams/mole
• The mass contributed by Oxygen (O) is: 16 grams/mole

The total mass of a water molecule is therefore: 2 (from H) + 16 (from O) = 18 grams/mole

The percentage of the mass that is Oxygen (O) can be found by dividing the mass of Oxygen by the total mass, and then multiplying by 100 to get a percentage:

(16 / 18) * 100 = 88.89%

So, Y = 88.89%. This means that 88.89% of the mass of a water molecule is due to Oxygen.