Among the triatomic molecules/ions, BeCl₂, $$N_3^-$$, N₂O, $$NO_2^+$$, O₃, SCl₂, $$ICl_2^-$$, $$I_3^-$$ and XeF₂, the total number of linear molecule(s)/ion(s) where the hybridization of the central atom does not have contribution from the d-orbital(s) is

[Atomic number: S = 16, Cl = 17, I = 53 and Xe = 54]

Not considering the electronic spin, the degeneracy of the second excited state( n = 3) of H atom is 9, while the degeneracy of the second excited state of H^– is ___________.

The total number of stereoisomers that can exist for M is ___________.

The number of resonance structure for N is _________.