What are the properties of elements??

Chemical properties

Atomic number. The atomic number indicates the number of protons within the core of an atom.

Atomic mass. The name indicates the mass of an atom, expressed in atomic mass units (AMU).

Electronegativity according to Pauling.

Density.

Melting point.

Boiling point.

Vanderwaal's radius.

Ionic radius.

And many more.

Explanation:

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%

the answer is b & c i believe : )