Correct order should be :    ii  <  i  <  iv < iii

(i) $\mathrm{N} \mathrm{is} {\mathrm{sp}}^3$hybridised, $1°$Amine without delocalization.

(ii) $\mathrm{N} \mathrm{is} {\mathrm{sp}}^2$ hybridised.

(iii) Guanidine is a stronger base than amidine (resonance stabilised)

(iv) $2°$ Amine, $\mathrm{N} \mathrm{is} {\mathrm{sp}}^3$ hybridised.