We've got a homework and I know this question may seem so primitive, but I have already read whole textbook and I've been looking also on the Internet, but I still cannot find the right answer. I'd be grateful if you could help me.
The question is what is the basic structural unit of an atom. I'm considering whether to take into account only proton since "a basic structural unit" of something is usually only one thing and also atom of hydrogen consists only of a single electron and proton. But on the other hand, neutrons make up quite a considerable part of weigh of other atoms and are a part of the nucleus.
The answer options are the following: a) atom b) proton c) neutron d) electron e) positronium