Number of paramagnetic complexes among the following is ____. $\left[\mathrm{MnBr}_{4}\right]^{2-}$, $\left[\mathrm{NiCl}_{4}\right]^{2-}$, $\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}$, $\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]$, $\left[\mathrm{CoF}_{6}\right]^{3-}$, $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}$, $\left[\mathrm{Mn}(\mathrm{CN})_{6}\right]^{3-}$, $\left[\mathrm{Ti}(\mathrm{CN})_{6}\right]^{3-}$, $\left[\mathrm{Cu}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$, $\left[\mathrm{Co}\left(\mathrm{C}_{2} \mathrm{O}_{4}\right)_{3}\right]^{3-}$

JEE Main · 2026 · 08 Apr 2026 · Shift 2 · Coordination Compounds

Number of paramagnetic complexes among the following is ____.

[MnBr_{4}]^{2 -}

[NiCl_{4}]^{2 -}

[Ni (CN)_{4}]^{2 -}

[Ni (CO)_{4}]

[CoF_{6}]^{3 -}

[Fe (CN)_{6}]^{4 -}

[Mn (CN)_{6}]^{3 -}

[Ti (CN)_{6}]^{3 -}

[Cu (H_{2} O)_{6}]^{2 +}

[Co (C_{2} O_{4})_{3}]^{3 -}

Answer: 6

A complex is paramagnetic when the central ion keeps unpaired electrons.

[MnB r_{4}]^{2 -}

(

M n^{2 +}, d^{5}

, weak-field, tetrahedral) has five,

[NiC l_{4}]^{2 -}

(

N i^{2 +}, d^{8}

, tetrahedral) has two,

[Co F_{6}]^{3 -}

(

C o^{3 +}, d^{6}

, high-spin) has four,

[Mn (CN)_{6}]^{3 -}

(

M n^{3 +}, d^{4}

, low-spin) has two,

[Ti (CN)_{6}]^{3 -}

(

T i^{3 +}, d^{1}

) has one and

[Cu (H_{2} O)_{6}]^{2 +}

(

C u^{2 +}, d^{9}

) has one; these six are paramagnetic.

[Ni (CN)_{4}]^{2 -}

(square-planar

d^{8}

[Ni (CO)_{4}]

(

d^{10}

[Fe (CN)_{6}]^{4 -}

(low-spin

d^{6}

) and

[Co (C_{2} O_{4})_{3}]^{3 -}

(low-spin

d^{6}

) have all electrons paired and are diamagnetic. The number of paramagnetic complexes is six.

JEE Main · 2026 · 08 Apr 2026 · Shift 2 · Integer answer