(2) For the instruments and medicines provided by the experimental platform, you think Xiaohong painted the preparation, collection and full inspection of O2, so the answer is: ④.
(3) Xiaohong's mistakes in completing the experiment include: adding drugs to the vertical tube mouth, which is easy to stick to the tube mouth or tube wall; It is impossible to verify whether the bottle is full by inserting a wooden strip with mars. Therefore, the answer is: adding medicine vertically to the test tube mouth is easy to stick to the nozzle or tube wall; It is impossible to verify whether the bottle is full by inserting a piece of wood with sparks.
(4) calcium carbonate and hydrochloric acid exchange components to generate calcium chloride, water and carbon dioxide, and then calcium carbonate and hydrochloric acid are balanced; If you add an alcohol lamp, you can also assemble a potassium permanganate oxygen generator, so the answer is: CaCO3+2HCl=CaCl2+CO2↑+H2O, alcohol lamp.