Q1 / 75 · JEE Main 2026 (21 January Shift 1) · Chemistry
Given below are two statements :
Statement I : Among $\left.\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+},\left[\mathrm{Ni}(\mathrm{en})_{3}\right)\right]^{2+},\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$ and $\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$, $\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ has the maximum number of unpaired electrons.
Statement II : The number of pairs among $\left\{\left[\mathrm{NiCl}_{4}\right]^{2-},\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\right\},\left\{\left[\mathrm{NiCl}_{4}\right]^{2-},\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\right\}$ and $\left\{\left[\mathrm{Ni}(\mathrm{CO})_{4}\right],\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\right\}$ that contain only diamagnetic species is two.
In the light of the above statements, choose the correct answer from the options given below : Statement I is true but Statement II is false Both Statement I and Statement II are false
Statement I : Among $\left.\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]^{2+},\left[\mathrm{Ni}(\mathrm{en})_{3}\right)\right]^{2+},\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$ and $\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$, $\left[\mathrm{Mn}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ has the maximum number of unpaired electrons.
Statement II : The number of pairs among $\left\{\left[\mathrm{NiCl}_{4}\right]^{2-},\left[\mathrm{Ni}(\mathrm{CO})_{4}\right]\right\},\left\{\left[\mathrm{NiCl}_{4}\right]^{2-},\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\right\}$ and $\left\{\left[\mathrm{Ni}(\mathrm{CO})_{4}\right],\left[\mathrm{Ni}(\mathrm{CN})_{4}\right]^{2-}\right\}$ that contain only diamagnetic species is two.
In the light of the above statements, choose the correct answer from the options given below : Statement I is true but Statement II is false Both Statement I and Statement II are false
- Correct answerAStatement I is true but Statement II is false
- BBoth Statement I and Statement II are false
- CBoth Statement I and Statement II are true
- DStatement I is false but Statement II is true
Solution
Statement I: Unpaired electrons in each complex:
$[Cu(NH_3)_4]^{2+}$: $Cu^{2+}$ is $d^9$ → 1 unpaired
$[Ni(en)_3]^{2+}$: $Ni^{2+}$ is $d^8$, octahedral → 2 unpaired
$[Ni(NH_3)_6]^{2+}$: $Ni^{2+}$ is $d^8$ → 2 unpaired
$[Mn(H_2O)_6]^{2+}$: $Mn^{2+}$ is $d^5$, weak field → high spin → 5 unpaired
$[Mn(H_2O)_6]^{2+}$ has maximum. Statement I is true.
Statement II: $[NiCl_4]^{2-}$: $Ni^{2+}$ ($d^8$), tetrahedral → paramagnetic
$[Ni(CO)_4]$: $Ni^0$ ($d^{10}$) → diamagnetic
$[Ni(CN)_4]^{2-}$: $Ni^{2+}$ ($d^8$), square planar → diamagnetic
Only pair $\{[Ni(CO)_4], [Ni(CN)_4]^{2-}\}$ has both diamagnetic. Count = 1, not 2. Statement II is false.
$[Cu(NH_3)_4]^{2+}$: $Cu^{2+}$ is $d^9$ → 1 unpaired
$[Ni(en)_3]^{2+}$: $Ni^{2+}$ is $d^8$, octahedral → 2 unpaired
$[Ni(NH_3)_6]^{2+}$: $Ni^{2+}$ is $d^8$ → 2 unpaired
$[Mn(H_2O)_6]^{2+}$: $Mn^{2+}$ is $d^5$, weak field → high spin → 5 unpaired
$[Mn(H_2O)_6]^{2+}$ has maximum. Statement I is true.
Statement II: $[NiCl_4]^{2-}$: $Ni^{2+}$ ($d^8$), tetrahedral → paramagnetic
$[Ni(CO)_4]$: $Ni^0$ ($d^{10}$) → diamagnetic
$[Ni(CN)_4]^{2-}$: $Ni^{2+}$ ($d^8$), square planar → diamagnetic
Only pair $\{[Ni(CO)_4], [Ni(CN)_4]^{2-}\}$ has both diamagnetic. Count = 1, not 2. Statement II is false.
Hence, the correct answer is option: 'A'.