Remember that there is a learning objective in your son's teacher’s mind when assigning him a project to complete and part of what she or he has in mind is to get your son engaged enough to go deeper than his textbook into some science content of his choosing. My advice is not for you (or me) to pick a topic for him simply because it is easy for him to do. Help him pick a topic that he is interested in and get him to make up his mind to really educate himself about it. I know that this is not what you wanted to hear, but I wouldn’t be doing you or your son much service to tell you what to do. Encourage him to challenge himself and really learn something!