Thank you for the opportunity to help you with your question!
Hi, nertigo! So a good way to learn oxidation reduction is OIL RIG: Oxidation Is Losing electrons, and Reduction Is Gaining electrons. So, we need to look to see what is losing electrons.
So, Bromine (2Br2) is LOSING electrons (OIL = oxidation) because it is binding to sodium in the product (NaBr) and Hydrogen (HBr). When sodium and hydrogen bind, it occupies the space that use to be filled with electrons.
Hope this helps! Let me know what questions you have.
Please let me know if you need any clarification. I'm always happy to answer your questions.
Jun 9th, 2015
Na2SO3 is also being oxidized to because it is gaining electrons (gets an extra Oxygen).
Na2SO3 --> Na2SO4 adds the two electrons from oxygen in the structure.