@ Istria- It looks like your professor gave you a few chemical compounds in a sentence and asked to write them out as a chemical formula. I can help you with Nitrous acid.
Nitrous acid is HNO2 (little two), and is an oxyacid. Oxyacids are just hydrogen molecules attached to a polyatomic ion containing oxygen. The rules for naming these are as simple as the rules given by Valley Fiah for naming binary acids. All you have to do is add the word acid, and switch the suffix. Unlike binary acids, you don't have to add hydro to the beginning of the word.
When you swap the suffixes just remember that -ate- is replaced by -ic- and -ite- is replaced by -ous-. So HNO3 (little three) is called nitric acid and HNO2 is called nitrous acid.