Fe+O2 yeilds Fe2O3 What kind of reaction is this?

Answer 1

Since you have two things combining to form one, it is a combination, also called synthesis, reaction.

Some chemists would also classify this reaction as a combustion, since you are combining iron with oxygen.

You could also classify it as a oxidation reduction reaction, since the iron is being oxidized and the oxygen is being reduced.

If you are simply studying the five basic types of chemical reactions, go with the combination or synthesis answer.

Answer 2

This is reaction of oxidation. 2Fe +3O2 = 2Fe2O3. This is what you see when iron gets corroded. That dark yellow color is actually Fe2O3 x nH20 . Fe2O3 is hygroscopic material it takes water from air.