How am I supposed to answer this?
Effectively, the question is giving the radii in some sort of reduced units, where it's expressing the size of each species relative to the size of something else.  

Thus one can interpret the choices in this question as providing relative sizes.  So, for instance, choice "A" says the ion is 2.60/.77 = 3.38 times the size of the neutral atom, and so on.  

Given your knowledge of the actual sizes of the ion and the neutral atom, you should now be able to choose the best answer.