Water has a density of $1.0 \mathrm{~g} / \mathrm{cm}^3$ at room temperature. State whether each of the following will sink or float when placed in water.
a. Paraffin wax (density $=0.90 \mathrm{~g} / \mathrm{cm}^3$ )
b. Limestone (density $=2.8 \mathrm{~g} / \mathrm{cm}^3$ )