Because the solid is soluble in water, it cannot be calcium fluoride.
This leaves us with either silver fluoride or potassium bromide, as both are soluble in water.
Upon addition of sodium sulfate, a white precipitate forms, confirming that the substance was silver fluoride as the precipitate are of silver sulfate.
I think it is calcium carbonate, from sedimentary rocks and such
The atomic number of calcium is 20 which means it has 20 protons and as an atom (not an ion) it also has 20 electrons. These are in four energy levels (1 though 4) .
Cotton is opaque. Opaque objects do not let light pass through. You can't see through the objects that are opaque.
