1) If calcium were to combine with the compound barium nitrate, which member of the barium nitrate would calcium replace?

Calcium would displace barium.

Explanation:

Ba (NO₃) ₂ + Ca - -> Ca (NO₃) ₂ + Ba

There are two types of compounds: molecular/covalent and ionic.

Molecular/covalent compounds are non-metal + non-metal.

Ionic compounds are metal + non-metal.

Looking at the periodic table, barium is a metal. Calcium is also a metal.

Checking a polyatomic ions chart would tell you NO₃⁻ is a non-metal because it has a negative charge.

Since there is no metal + metal compound, the calcium metal would displace barium. The compound remains ionic.