JEE Main 2025 Jan 28 Shift 2, Chemistry Q25: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Jan 28, Shift 2Chemistry

Total number of molecules/species from following which will be paramagnetic is ______.

$O_{2}$ , $O_{2}^{+}$ , $O_{2}^{-}$ , $N O$ , $N O_{2}$ , $C O$ , $K_{2} [N i C l_{4}]$ , $[C o (N H_{3})_{6}] C l_{3}$ , $K_{2} [N i (C N)_{4}]$

Your answer

Solution

Checking each species for unpaired electrons:

$O_{2}$ : MOT gives 2 unpaired electrons in $π^{*}$ orbitals. Paramagnetic.

$O_{2}^{+}$ (15 electrons): 1 unpaired electron. Paramagnetic.

$O_{2}^{-}$ (17 electrons): 1 unpaired electron. Paramagnetic.

$N O$ (15 valence electrons): odd electron species, 1 unpaired electron. Paramagnetic.

$N O_{2}$ (17 valence electrons): odd electron species. Paramagnetic.

$C O$ : all electrons paired. Diamagnetic.

$K_{2} [N i C l_{4}]$ : $N i^{2 +}$ ( $d^{8}$ ) with weak-field $C l^{-}$ , tetrahedral, 2 unpaired electrons. Paramagnetic.

$[C o (N H_{3})_{6}] C l_{3}$ : $C o^{3 +}$ ( $d^{6}$ ) with strong-field $N H_{3}$ , all paired. Diamagnetic.

$K_{2} [N i (C N)_{4}]$ : $N i^{2 +}$ ( $d^{8}$ ) with strong-field $C N^{-}$ , square planar, all paired. Diamagnetic.

Paramagnetic count $= 6$ (namely $O_{2}$ , $O_{2}^{+}$ , $O_{2}^{-}$ , $N O$ , $N O_{2}$ , $K_{2} [N i C l_{4}]$ ).

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