Copper sulphate reacts with sodium hydroxide to form a blue precipitate of copper hydroxide and sodium sulphate. In an experiment, `15.95 g` of copper sulphate reacted with `8.0` g sodium hydroxide to form `9.75 g` of copper hydroxide and 14.2 g of sodium sulphate. Which law of chemical conbination is illustrated by this data ? Give reason for your choice.