Answers (1)
You do have a printed periodic table, right? You can get the information at www.chemicalelements.com/index.html or wikipedia.com but you really need your own printed copy to carry with you. It will be a primary reference for everything you do.
Barium has 56 protons, 3.1 times as many as oxygen. So you would expect any compound of barium to be at least three times as dense as water, and more because barium also has 74 to 82 neutrons. Sulfur has 16 protons, twice as many as oxygen. You could if you wish count up all the protons and neatrons in barium, sulfur, oxygen, and water, and calculate a specific gravity for each isotope.