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Which of the following is iso-electronic : -
A
$CO_2$, $NO_2$
B
$NO_2^-$, $CO_2$
C
$CN^-$, CO
D
$SO_2$, $CO_2$
Detailed Solution
Isoelectronic species have the same total number of electrons.
$CN^-$: C (6) + N (7) + 1 = 14 electrons; CO: C (6) + O (8) = 14 electrons. They are isoelectronic.
$CO_2$: 6 + 16 = 22; $NO_2$: 7 + 16 = 23; $NO_2^-$: 24; $SO_2$: 16 + 16 = 32. These pairs do not match.
So $CN^-$ and CO are isoelectronic (both also isoelectronic with $N_2$).
$CN^-$: C (6) + N (7) + 1 = 14 electrons; CO: C (6) + O (8) = 14 electrons. They are isoelectronic.
$CO_2$: 6 + 16 = 22; $NO_2$: 7 + 16 = 23; $NO_2^-$: 24; $SO_2$: 16 + 16 = 32. These pairs do not match.
So $CN^-$ and CO are isoelectronic (both also isoelectronic with $N_2$).