Which of the molecules or ions are iso-structural and why?
`BF_(3),NH_(4)^(+),CO_(3)^(2-),BF_(4)^(-),NO_(3)^(-),CH_(3)^(+),C Cl_(4)`

Explanation

(i) `BF_(3).CH_(3)^(+)`-trigonal planar geometry.
The central atom undergoes `sp^(2)`-hybridisation forming `3sigma` bonds with the neighbouring atoms.
(ii) `NH_(4)^(+),C Cl_(4),BF_(4)^(-)`-tetrahedral geometry.
The central atom undergoes `sp^(3)`-hybridisation forming `4sigma` bonds with the neighbouring atoms.
(iii) `NO_(3)^(-),CO_(3)^(2-)`-trigonal planarr geometry.
The central atom is `sp^(2)`-hybridised forming `3sigma` bond and `1pi` bond.