Question

why NA+HAS SMALLER SIZE THAN NA

Answer 1

actually configuration of Na is 1s^2,2s^2,2p6,3s^1 , but Na+ configuration is 1s^2,2s^2,2p^6,
here we see Na+ have 3s subshell absent but in Na 3s subshell present , due to absent of 3s subshell in Na+ nucleus attract more electrostatic force and reduced the size of Na+
so, Na+ is smaller then Na

Answer 2

Na has electronic configuration 2, 5  
it has same no. of protons and electrons
Na+ has lost one electron which means no. of protons in the nucleus is more than the no. of electrons. thus, it pulls the electron more closer to itself.
that is why Na+ has a smaller size than Na