You need to find out these for the substances you’re asking about (for instance, the specific gravity/density of water = 1). Some substance (such as lead) would have a higher specific gravity/density (it’s heavier) – I don’t know the exact value, but since it’s heavier, it’ll be more than 1. So think of this as “the higher number will sink, the lower number will float”. Once you know the values for the substances (you’ll probably find them in your text, if not, look them up on the internet), you can calculate which each will do. CAUTION: ice and water each have a different specific gravity/density – use the correct one!