Arginine (Arg, R) – Basic side chain: 3-Guanidinopropyl group.

This cation is stabilized by delocalization (notice that the carbon, nitrogen, and hydrogen atoms of the guanidine group are all co-planar!).  Which atom in the side chain carries a formal positive charge in the structure shown?  (Look at the ball & stick or skeletal model.)  There are two other resonance structures for the side chain.  Can you draw them?