The reaction, Fe2O3 + 3CO------> 2Fe + 3CO2 is an oxidation-reduction reaction.
An oxidation-reduction reaction is a reaction in which there is a change in oxidation number from left to right in the reaction. This is because, a specie is oxidized and another specie is reduced.
In the reaction; Fe2O3 + 3CO------> 2Fe + 3CO2, we can see that the oxidation number of iron decreased from +3 on the left hand side to zero on the right hand side. The oxidation number of carbon was increased from + 2 to +4.
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<em>I think that the answer is C.)</em>
<em>It makes the most sense because one or two of the other options talk about the sun getting closer to the earth which makes no sense. Also, the Earth's spinning speed does not slow down so that rules out option B. Lastly, the answer cannot be A whereas the sun's light does not fade, rather the Earth spins with a shadow casting over its back due to no sunlight on that facing side.</em>
<em>Hope this helps and have a nice day.</em>
<em>-R3TR0 Z3R0</em>
Control or controlled group is the part of the experiment where conditions are kept the same.