I have been asked to write academic assignments which require a formal style of writing. But I don't know what words and phrases are considered formal and what aren't. Is there any way I can learn and check it?
Many thanks.
I don't think there is any list which divides words into "formal" and "informal". However, there are some common sense guidelines which I would advise you to follow when writing your assignments - or, indeed, any written communication which needs to be clear and unambiguous.
Do not use slang words or the sort of abbreviations which are commonly used when texting by phone, for example,"ru" for "are you" and so on. Pay attention to your grammar, so that your meaning is clear, and always re-read your draft so that you can spot and eliminate the sort of errors that I have corrected in red above. Do not confuse "formal" with using stilted, "flowery", language, such as "I was at pains to observe.." when you mean "I saw..". The best formal writing uses simple words in short sentences. If you Google the "Economist Style Guide", you will find an excellent set of guidelines for writing clear English. I used to work in a British government department of state, and we employed the Economist Style Guide to help us draft ministerial submissions. Writing does not get much more formal than that!