# Which of the following are isoelectronic and isostructural?

$\begin{array}{1 1}(a)\;NO_3^-,CO_3^{2-}&(b)\; SO_3,NO_3^-\\(c)\;CO_3^{2-},SO_3&(d)\;ClO_3^{-},CO_3^{2-}\end{array}$

$NO_3^-$ and $CO_3^{2-}$ are isoelectronic and isostructural.
Hence (a) is the correct answer.