1.Which of the following are considered pure substances

heterogeneous mixtures
homogenous mixtures
elements only
elements and compounds

2. Ionic compounds are often formed when a metal atom bonds with a nonmetal atom.Which of the following is an ionic compound and why?

h2O, because both atoms are nonmetals
NH3, because both atoms are nonmetals
NaCI, because sodium is a metal and chlorine is a nonmetal
Na, because sodium is a metal

3.Covalent compounds are formed when two different nonmetals are chemically combined. Which of the following is a covalent compound and why?

h2O, because H and O are two different nonmetals
H, because it is a nonmetal
NaCI, because sodium is a metal and chlorine is a nonmetal
O, because it is a nonmetal