Wax is a nonpolar substance. in which type of substance is it the most soluble? a. a cold nonpolar solvent b. a cold polar solvent c. a hot nonpolar solvent d. a hot polar solvent

Probably if the wax is in a molten state a hot non-polar solvent would be best. Heat  vegetable oil would be the best way to dissolve the molten wax.

Second question.

I actually think the ice forms on the top because it is less dense than the water. Good thing too. Fish would be frozen solid in winter if ice sank rather than floated as most other substances behave.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%