Given below are two statements:
Statement I: Among [mathrmCu(mathrmNH_3)_4]^2+$[\mathrm{Cu}(\mathrm{NH}_{3})_{4}]^{2+}$, [mathrmNi(mathrmen)_3]^2+$[\mathrm{Ni}(\mathrm{en})_{3}]^{2+}$, [mathrmNi(mathrmNH_3)_6]^2+$[\mathrm{Ni}(\mathrm{NH}_{3})_{6}]^{2+}$ and [mathrmMn(mathrmH_2mathrmO)_6]^2+$[\mathrm{Mn}(\mathrm{H}_{2}\mathrm{O})_{6}]^{2+}$, [mathrmMn(mathrmH_2mathrmO)_6]^2+$[\mathrm{Mn}(\mathrm{H}_{2}\mathrm{O})_{6}]^{2+}$ has the maximum number of unpaired electrons.
Statement II: The number of pairs among \[NiCl_4]^2-, [Ni(CO)_4]\$\{[NiCl_{4}]^{2-}, [Ni(CO)_{4}]\}$, \[NiCl_4]^2-, [Ni(CN)_4]^2-\$\{[NiCl_{4}]^{2-}, [Ni(CN)_{4}]^{2-}\}$ and \[Ni(CO)_4], [Ni(CN)_4]^2-\$\{[Ni(CO)_{4}], [Ni(CN)_{4}]^{2-}\}$ that contain only diamagnetic species is two.
In the light of the above statements, choose the correct answer from the options given below:
A.textStatement I is false but Statement II is true$\text{Statement I is false but Statement II is true}$
B.textBoth Statement I and Statement II are true$\text{Both Statement I and Statement II are true}$
C.textBoth Statement I and Statement II are false$\text{Both Statement I and Statement II are false}$
D.textStatement I is true but Statement II is false$\text{Statement I is true but Statement II is false}$
Solution & Explanation
### Core Logic
Evaluating Statement I:
- [Cu(NH_3)_4]^2+$[Cu(NH_3)_4]^{2+}$: Cu^2+$Cu^{2+}$ is 3d^9$3d^9$, 1 unpaired electron.
- [Ni(en)_3]^2+$[Ni(en)_3]^{2+}$: Ni^2+$Ni^{2+}$ is 3d^8$3d^8$, in octahedral field, 2 unpaired electrons.
- [Ni(NH_3)_6]^2+$[Ni(NH_3)_6]^{2+}$: Ni^2+$Ni^{2+}$ is 3d^8$3d^8$, 2 unpaired electrons.
- [Mn(H_2O)_6]^2+$[Mn(H_2O)_6]^{2+}$: Mn^2+$Mn^{2+}$ is 3d^5$3d^5$, weak field ligand H_2O$H_2O$ leads to high spin, 5 unpaired electrons.
So [Mn(H_2O)_6]^2+$[Mn(H_2O)_6]^{2+}$ has the maximum number of unpaired electrons. Statement I is true.
Evaluating Statement II:
- [Ni(CO)_4]$[Ni(CO)_4]$: Ni(0)$Ni(0)$ is 3d^8 4s^2$3d^8 4s^2$, strong field CO pairs electrons to 3d^10$3d^{10}$, diamagnetic (0 unpaired).
- [Ni(CN)_4]^2-$[Ni(CN)_4]^{2-}$: Ni^2+$Ni^{2+}$ is 3d^8$3d^8$, strong field CN^-$CN^-$ forces pairing rightarrow dsp^2$\rightarrow dsp^2$ square planar, diamagnetic (0 unpaired).
- [NiCl_4]^2-$[NiCl_4]^{2-}$: Ni^2+$Ni^{2+}$ is 3d^8$3d^8$, weak field Cl^-$Cl^-$ does not pair rightarrow sp^3$\rightarrow sp^3$ tetrahedral, paramagnetic (2 unpaired).
The pairs containing ONLY diamagnetic species:
- \[NiCl_4]^2-, [Ni(CO)_4]\$\{[NiCl_4]^{2-}, [Ni(CO)_4]\}$rightarrow$\rightarrow$ 1 para, 1 dia (No)
- \[NiCl_4]^2-, [Ni(CN)_4]^2-\$\{[NiCl_4]^{2-}, [Ni(CN)_4]^{2-}\}$rightarrow$\rightarrow$ 1 para, 1 dia (No)
- \[Ni(CO)_4], [Ni(CN)_4]^2-\$\{[Ni(CO)_4], [Ni(CN)_4]^{2-}\}$rightarrow$\rightarrow$ Both dia (Yes)
The number of such pairs is exactly ONE. Statement II says two, so it is false.
### Step 1: Final Conclusion
Statement I is true, Statement II is false.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Keywords:#Magnetic Properties#unpaired electrons#JEE Main 2026 Morning Q65#Coordination Compounds JEE Main 2026
More Coordination Compounds Previous-Year Questions — Page 10
Q80jee_main_2024_30_jan_morningLigands and Coordination Number
Choose the correct Statements from the following:
(A) Ethane-1 2-diamine is a chelating ligand.
(B) Metallic aluminium is produced by electrolysis of aluminium oxide in presence of cryolite.
(C) Cyanide ion is used as ligand for leaching of silver.
(D) Phosphine act as a ligand in Wilkinson catalyst.
(E) The stability constants of Ca^2+$Ca^{2+}$ and Mg^2+$Mg^{2+}$ are similar with EDTA complexes.
Choose the correct answer from the options given below:
### Core Logic
(A) Ethane-1,2-diamine (en) is a bidentate ligand. Because it coordinates through two nitrogen atoms to the same metal ion, it forms a ring, making it a chelating ligand. (True)
Ligands and Coordination Number solution diagram for Q80 - JEE Main 2024 Morning
(B) In the Hall-Heroult process, metallic aluminium is produced by the electrolysis of molten alumina (Al_2O_3$Al_2O_3$). Cryolite (Na_3AlF_6$Na_3AlF_6$) is added to lower the melting point and increase conductivity. (True)
(C) In the extraction of silver (MacArthur-Forrest cyanide process), Ag$Ag$ ore is leached with a dilute solution of NaCN$NaCN$ or KCN$KCN$ in the presence of air to form the soluble complex [Ag(CN)_2]^-$[Ag(CN)_2]^-$. Thus, cyanide acts as a ligand. (True)
Ag_2S + NaCN rightleftharpoons Na[Ag(CN)_2] + Na_2S$$Ag_2S + NaCN \rightleftharpoons Na[Ag(CN)_2] + Na_2S$$
(D) Wilkinson's catalyst is [RhCl(PPh_3)_3]$[RhCl(PPh_3)_3]$. The ligand is triphenylphosphine (PPh_3$PPh_3$), not phosphine (PH_3$PH_3$). (False)
(E) The stability constant of the Ca^2+$Ca^{2+}$-EDTA complex is significantly higher than that of the Mg^2+$Mg^{2+}$-EDTA complex, which is why EDTA is used to estimate hardness sequentially. They are not similar. (False)
### Step 1: Conclusion
Only statements (A), (B), and (C) are correct.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Class 12 Chemistry: General Principles and Processes of Isolation of Elements
Q61jee_main_2024_31_jan_eveningCrystal Field Theory
Match List-I with List-II.
List - I (Complex ion)
List - II (Electronic Configuration)
A. [Cr(H_2O)_6]^3+$[Cr(H_2O)_6]^{3+}$
I. t_2g^2e_g^0$t_{2g}^2e_g^0$
B. [Fe(H_2O)_6]^3+$[Fe(H_2O)_6]^{3+}$
II. t_2g^3e_g^0$t_{2g}^3e_g^0$
C. [Ni(H_2O)_6]^2+$[Ni(H_2O)_6]^{2+}$
III. t_2g^3e_g^2$t_{2g}^3e_g^2$
D. [V(H_2O)_6]^3+$[V(H_2O)_6]^{3+}$
IV. t_2g^6e_g^2$t_{2g}^6e_g^2$
Choose the correct answer from the options given below:
### Core Logic
Identify the central metal ion, its oxidation state, and outer electronic configuration:
1) [Cr(H_2O)_6]^3+$[Cr(H_2O)_6]^{3+}$ contains Cr^3+ : [Ar] 3d^3$Cr^{3+} : [Ar] 3d^3$. In an octahedral field with weak field ligands (H_2O$H_2O$), the configuration is t_2g^3 e_g^0$t_{2g}^3 e_g^0$.
2) [Fe(H_2O)_6]^3+$[Fe(H_2O)_6]^{3+}$ contains Fe^3+ : [Ar] 3d^5$Fe^{3+} : [Ar] 3d^5$. With weak field ligand (H_2O$H_2O$), it forms a high spin complex: t_2g^3 e_g^2$t_{2g}^3 e_g^2$.
3) [Ni(H_2O)_6]^2+$[Ni(H_2O)_6]^{2+}$ contains Ni^2+ : [Ar] 3d^8$Ni^{2+} : [Ar] 3d^8$. In an octahedral field, the configuration is t_2g^6 e_g^2$t_{2g}^6 e_g^2$.
4) [V(H_2O)_6]^3+$[V(H_2O)_6]^{3+}$ contains V^3+ : [Ar] 3d^2$V^{3+} : [Ar] 3d^2$. In an octahedral field, the configuration is t_2g^2 e_g^0$t_{2g}^2 e_g^0$.
### Step 1: Final Mapping
A rightarrow$\rightarrow$ II (t_2g^3e_g^0$t_{2g}^3e_g^0$)
B rightarrow$\rightarrow$ III (t_2g^3e_g^2$t_{2g}^3e_g^2$)
C rightarrow$\rightarrow$ IV (t_2g^6e_g^2$t_{2g}^6e_g^2$)
D rightarrow$\rightarrow$ I (t_2g^2e_g^0$t_{2g}^2e_g^0$)
This matches option (4).
### Pattern Recognition
Shortcut: Vanadium (V) in +3$+3$ state has 2$2$ electrons, so D rightarrow I$D \rightarrow I$. Only options (1) and (4) have D rightarrow I$D \rightarrow I$. Nickel (Ni) in +2$+2$ state has 8$8$ electrons, so C rightarrow IV$C \rightarrow IV$. Only option (4) has C rightarrow IV$C \rightarrow IV$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Q68jee_main_2024_31_jan_eveningMagnetic Properties of Complexes
Select the option with correct property -
A.text(1) [Ni(CO)_4]text and [NiCl_4]^2-text both diamagnetic$\text{(1) }[Ni(CO)_4]\text{ and }[NiCl_4]^{2-}\text{ both diamagnetic}$
B.text(2) [Ni(CO)_4]text and [NiCl_4]^2-text both paramagnetic$\text{(2) }[Ni(CO)_4]\text{ and }[NiCl_4]^{2-}\text{ both paramagnetic}$
### Core Logic
For [Ni(CO)_4]$[Ni(CO)_4]$:
Nickel is in 0$0$ oxidation state: Ni^0 = [Ar] 3d^8 4s^2$Ni^0 = [Ar] 3d^8 4s^2$. CO$CO$ is a strong field ligand, forcing pairing of electrons. The 4s$4s$ electrons move to the 3d$3d$ orbital, making the configuration 3d^10$3d^{10}$. With no unpaired electrons, the hybridization is sp^3$sp^3$ and it is diamagnetic.
For [NiCl_4]^2-$[NiCl_4]^{2-}$:
Nickel is in +2$+2$ oxidation state: Ni^2+ = [Ar] 3d^8$Ni^{2+} = [Ar] 3d^8$. Cl^-$Cl^-$ is a weak field ligand, so pairing does not occur against Hund's rule. The configuration remains t_2g^6 e_g^2$t_{2g}^6 e_g^2$ (or simply two unpaired electrons in the tetrahedral d$d$ splitting). The hybridization is sp^3$sp^3$ and with 2 unpaired electrons, it is paramagnetic.
### Step 1: Final Conclusion
[Ni(CO)_4]$[Ni(CO)_4]$ is diamagnetic, while [NiCl_4]^2-$[NiCl_4]^{2-}$ is paramagnetic. This correctly corresponds to option (4).
### Pattern Recognition
Strong field ligands (like CO$CO$, CN^-$CN^-$) usually lead to diamagnetism in d^8$d^8$ metal ions by forming square planar (dsp^2$dsp^2$) or forcing d^10$d^{10}$ configurations (for Ni^0$Ni^0$). Weak field halogens lead to paramagnetic sp^3$sp^3$ complexes for Ni(II)$Ni(II)$.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
Q76jee_main_2024_31_jan_morningVBT and CFT
The correct statements from following are:
A. The strength of anionic ligands can be explained by crystal field theory.
B. Valence bond theory does not give a quantitative interpretation of kinetic stability of coordination compounds.
C. The hybridization involved in formation of [Ni(CN)_4]^2-$[Ni(CN)_4]^{2-}$ complex is dsp^2$dsp^2$
D. The number of possible isomer(s) of cis-[PtCl_2(en)_2]^2+$cis-[PtCl_2(en)_2]^{2+}$ is one
Choose the correct answer from the options given below:
A.textA, D only$\text{A, D only}$
B.textA, C only$\text{A, C only}$
C.textB, D only$\text{B, D only}$
D.textB, C only$\text{B, C only}$
Solution
### Step 1: Analyzing Statement A
Crystal field theory considers ligands as point charges. Therefore, anionic ligands should exert the greatest splitting effect, but practically they are at the lower end of the spectrochemical series. CFT cannot explain this properly. Hence, Statement A is incorrect.
### Step 2: Analyzing Statement B
Valence bond theory (VBT) is qualitative and does not give a quantitative interpretation of either thermodynamic or kinetic stability. Hence, Statement B is correct.
### Step 3: Analyzing Statement C
In [Ni(CN)_4]^2-$[Ni(CN)_4]^{2-}$, Ni$Ni$ is in +2$+2$ state (3d^8$3d^8$). Since CN^-$CN^-$ is a strong field ligand, pairing of electrons takes place leaving one inner 3d orbital empty. Thus, the hybridization is dsp^2$dsp^2$ (square planar). Hence, Statement C is correct.
### Step 4: Analyzing Statement D
cis-[PtCl_2(en)_2]^2+$cis-[PtCl_2(en)_2]^{2+}$ is an octahedral complex of type M(AA)_2a_2$M(AA)_2a_2$. The cis-isomer lacks a plane of symmetry and is optically active, thus it exists as a pair of enantiomers (d and l). Therefore, the number of possible isomers is 2, not 1. Statement D is incorrect.
### Final Conclusion
Statements B and C are correct.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
The 'Spin only' Magnetic moment for [Ni(NH_3)_6]^2+$[Ni(NH_3)_6]^{2+}$ is ________ times 10^-1$\times 10^{-1}$ BM.
(given = Atomic number of Ni: 28)
Numerical Answer.Answer: 28 to 28
Solution
### Related Formula
mu = sqrtn(n + 2) text BM$$\mu = \sqrt{n(n + 2)} \text{ BM}$$
### Step 1: Electronic Configuration
Atomic number of Ni = 28$Ni = 28$.
Ni^2+ = [Ar] 3d^8$Ni^{2+} = [Ar] 3d^8$
Because the geometry is octahedral (coordination number 6) and NH_3$NH_3$ acts as a weak field ligand with Ni^2+$Ni^{2+}$ (or because d^8$d^8$ configuration always has 2 unpaired electrons in an octahedral field regardless of ligand strength):
The configuration in the t_2g$t_{2g}$ and e_g$e_g$ levels is t_2g^6 e_g^2$t_{2g}^6 e_g^2$.
### Step 2: Calculating Magnetic Moment
Number of unpaired electrons, n = 2$n = 2$.
mu = sqrt2(2 + 2) = sqrt8 approx 2.828 text BM$$\mu = \sqrt{2(2 + 2)} = \sqrt{8} \approx 2.828 \text{ BM}$$
Representing in 10^-1$10^{-1}$ scale:
mu approx 28.28 times 10^-1 text BM$$\mu \approx 28.28 \times 10^{-1} \text{ BM}$$
Rounding to the nearest integer as typically expected gives 28.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 12 Chemistry: Coordination Compounds
More Coordination Compounds Questions — jee_main_2026_21_jan_morning
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