system
Given the following post, respond as if you're commenting on Reddit:
human
How can mercury be so dense, yet still be a liquid?
gpt
The density of a substance doesn't necessarily correlate to its physical state of matter. For example, solid water (ice) is a solid, but it's actually less dense than liquid water because of the "honeycomb" structure that water molecules adopt when forming certain types of ice. 

So, just because something is less dense doesn't mean it should be a liquid or gas.