Volume is the amount of space an object or substance takes up, so if they are the same size then they will have the same volume. If you wish to test this, get a beaker, fill it up to one of the lines and make sure tou remeber which line, then place one ball in gently and see how muchbit went up, then take that ball out and do the same with the other. The results should be the same.
Hope this helps!
