A 25.3-8 sample of an unknown compound contains 0.8 g of oxygen. What is the percent by mass of
oxygen in the compound?

The percentage by mass of oxygen in the 25.3 g sample of the unknown compound is 3.16%

From the question given above, the following data were obtained:

Mass of compound = 25.3 g

Mass of oxygen = 0.8 g

The percentage of oxygen in the compound can be obtained as follow:

Percentage of oxygen =

Thus, the percentage of oxygen in the compound is 3.16%

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specific gravity is the density of a substance divided by the density of water. since (at standard temperature and pressure) water has a density of 1 gram/cm3, and since all of the units cancel, specific gravity is usually very close to the same value as density

so "c" is the answer

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nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.