Water has a density of precisely 1 g/ml. Anything with a lesser density will float, anything more dense will sink. For example, steel is very heavy in comparison to water, nearly 8 g/cm^3 versus the 1. So steel sinks in water very quickly.
For #9, pick out any of the materials with a density below 1 g/cm^3.
For #10, I'd start with a list to make it easier. Write down the materials given in #9 and write them in order of lightest to heaviest material. In a graduated cylinder, the most dense material would be at the bottom while the least dense material will remain at the top. Draw and label the layers and you're done!
