Well! here is a short quick reply..!!
I was pretty sure that the lewis stucture of $\ce{HNO3}$ would be the one with 0 formal charge and than I found this. Though this link only shows how to calculate formal charge on $\ce{HNO3}$ but it gives a little hint.
Secondly a thought came to my mind that if you will focus on Resonance, there will be double bond character on both bonds between N & O.
