How do I identify the reducing agent in a redox reaction

If you can identify the species that was being oxidized, its species that contains the element on the other side is the reducing agent.

For example, in the equation Zn + Cu2+ --> Zn2+ + Cu, the zinc was oxidized, making Zn the reducing agent.

answer is: naturally occurring solid, inorganic compound or element is mineral.

minerals usually have crystalline form, that means than crystal constituents (atoms, molecules or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

for example magnetite is a mineral of iron oxide (fe₂o₃).

calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (caco₃).

dolomite is an   carbonate mineral composed of calcium magnesium carbonate (camg(co₃)₂).

im pretty sure its b