Question: how dense is a black hole?
Answer: The density at the center of a black hole is infinite (it's a famous "singularity", which leads to difficulties in modern cosmology). On Earth, densities range from 10-4 g/cm3 for light gases to 0.001 g/cm3 for aerogels and up to the heaviest substance, osmium, with a density of 22.61 g/cm3.