The plot of orbital wave function vs distance ‘r’ from the nucleous is given below.  The atomic orbital is

         

• Graph of ∣Ψ²∣ v/s r, touches r axis at 1 point so it has one radial node and since at r=0, it has some value so it should be for 's' orbital.

n-l-1  =1where l=0 $\Rightarrow$n-1 =1

∴ n=2 

2S orbital