Q.
Write the Lewis dot structural formula for each of
the following. Give also, the formula of a neutral
molecule, which has the same geometry and the same
arrangement of the bonding electrons as in each of the
following. An example is given below in the case of $H_3 O^+$
and $NH_3.$
(i) $O_2^{2-} (ii) CO_3^{2-}$
(iii)$CN^- (iv) NCS^-$

IIT JEEIIT JEE 1983
Solution:
Please refer the image for the solution explanation