The chemical equation here describes a reaction between barium carbonate and nitric acid.

BaCO3(s) + HNOz3(l) → Ba(NO3)2(aq) + CO2(g) + H2O(l)

Which statement most accurately identifies a reactant in the solid state?

a. BaCO3
b. HNO3
c. Ba(NO3)2
d. CO2