To determine the mass of oxygen in the sample, we can use the fact that the total mass of the sample is equal to the sum of the masses of carbon, hydrogen, and oxygen.
Given that the sample contains 0.6544 g of carbon (C) and 0.05503 g of hydrogen (H), we can calculate the mass of oxygen (O) as follows:
Mass of oxygen (O) = Total mass of the sample - Mass of carbon (C) - Mass of hydrogen (H)
Total mass of the sample = 1.00 g
Mass of oxygen (O) = 1.00 g - 0.6544 g - 0.05503 g
Mass of oxygen (O) = 0.29057 g
Therefore, the mass of oxygen in the sample is approximately 0.291 g, considering the significant figures in the given values.