Which liquid is the most dense? Which is least dense? How do you know?

 liquid hydrogen is the  least dense liquid because it's at about 70g/liter (. 07g/cm 3), mercury is most dense because mercury is dense because its heavy iron core amounts to nearly two-thirds of the planet's mass

air quality

poor drinking water

and heavy polution

can lead to poor health

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).