How does th composition of a mixture of hydrogen and oxygen differ from the composition of a compound containing hydrogen and oxygen?

mixture is going to have multiple different compounds inside it. So you might have a mixture of hydrogen gas (H2) and oxygen gas (O2) - each gas is a separate compound. If both hydrogen and oxygen are part of the same compound, then you only need one compound (e. g. H2O). A mixture may be homogeneous or heterogeneous depending on how well what you're mixing blend together, but a compound will be homogeneous because it's just one thing.