Why can't you change the subscripts in a formula in order to balance a chemical equation?

The subscripts determine what the chemicals are, you have to change the amount of the reactants/products rather than change what the reactants/products actually are
eg O2 is oxygen gas, if you wanted 4 of them to balance it it would have to be 2 O2 otherwise it wouldnt be oxygen gas any more :)

10.063g / 10.00 ml = 1.0063 g/ml which rounds off to 4 sig figs as: 1.006 g/ml

The answer would be