Hmm, haven't really thought of that before! Well, I guess they can both be a type of level, but each has a more specific usage. For instance, grade is used to describe a school grade (like 12th grade), or also for a type of quality inl. level, like top-grade produce. As for rank, I guess it's more about position, such as military rank or player ranking in sports. Hope this helps!

great answer thanx a lot bro