Answer:
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.
Answer: iron (oxides of iron)
Explanation: manganese nodules usually contain layers of iron and manganese oxides in a concentric arrangement and are called polymetallic nodules.
Answer:

Explanation:
Hello,
In this case, the molar enthalpy of reaction is obtained by dividing the involved energy by the reacting moles:

Thus, it is important to notice that the compound "uses" the energy, it means that it absorbs the energy, for that reason the sign is positive. Moreover, computing the result in kJ/mol we finally obtain:

Best regards.
The answer would be 2+ since the atomic number represents how many protons are in the element. In this case, there are 16 protons, but only 14 electrons, which means there are an additional 2 protons, hence the 2+ charge on the ion.