Question

A sample of pure water, whatever the sources always contains......by mass of oxygen and 11.1% by mass of hydrogen
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Answer 1

Answer:

88.9%................︻デ═一

Answer 2

Answer:88.4%

Explanation:
According to the law of definite proportions or constant composition, in all the pure samples of a particular chemical compound, the constituent elements are generally combined in the same proportions by mass.

The combination is regardless of the mode or origin of the of the compound.

A sample of pure water,whatever the source will be, will always contain 88.8% by mass of oxygen and  11.1% as the mass of hydrogen.
Both the gases are divided in a constant ratio. Since, H2O contains the elements H and O in a fixed ratio by mass, this explains the law of constant composition, thus they are divided in a ratio of 1:8.
Thus, the mass of Oxygen is 88.8%.