I'd say B, 2 reactions. Calcite is defined as [tex] CaCO_{3} [/tex], and carbonic acid as [tex] H_{2} C O_{3} [/tex].
The usual reaction would be to mix both components, obtaining the following:
[tex] CaCO_{3} [/tex] + [tex] H_{2} C O_{3} [/tex] = [tex] Ca^{2+} + 2HCO_{3} ^{-} [/tex]
Which means we have 2 reactions. Nevertheless, to give you a full explanation, I'd need more information to be sure you're not talking about a reaction with other components involved.
