If a sample of a different compound decomposes into 0.429 g of carbon and 0.571 g of oxygen, what is its ratio of the mass of o to c

Ratio is the relationship between two number indicating how many times the first number containing the second number.

The ratio of carbon to oxygen is as follows

0.429 : 0.571

multiply 1000 to remove the decimals

therefore the ratio of mass of carbon to mass of oxygen = 429:571