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All questions of Coordination Compounds for NEET Exam

If zeise’s salt has the formula [Pt(C2H4)CI3]-. In this, platinum primary and secondary valency are
  • a)
    + 1 and 3
  • b)
    + 1 and 4
  • c)
    + 3 and 4
  • d)
    + 4 and 6
Correct answer is option 'B'. Can you explain this answer?

Krishna Iyer answered
Let the oxidation state of pt be x.
Oxidation state of cl is -1.
So x + 0 – (1*3) must be equal to -1 since the charge of the whole compound is -1.
x + 0 – (1*3) = -1
x -3 = -1
x = -1 + 3
x = +2
So the oxidation state of platinum is +2.
Secondary is due to legend there are mono deadened legend 
then 1×4= 4
 
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The correct IUPAC name of the complex Fe(C5H5)2 is _
  • a)
    Cyclopentadienyl iron (II)
  • b)
    Bis (cyclopentadienyl) iron (II)
  • c)
    Dicyclopentadiency ferrate (II) 
  • d)
    Ferrocene
Correct answer is option 'B'. Can you explain this answer?

Alok Mehta answered
The iron complex may be treated as cationic part, and C5H5- is a bidentate ligand therefore name can be assigned as follows “dicyclopentadienyl Iron (II) cation”.

Type of bonding in K4 [Fe(CN)6] is/a
  • a)
    ionic
  • b)
    covalent
  • c)
    metallic
  • d)
    coordinate covalent
Correct answer is option 'A,B,D'. Can you explain this answer?

Shubham Jain answered
The complex K4[Fe(CN)6] whose formula can be written like that of double salt. Fe(CN)2 . 4KCN, dissociates to give K+ and [Fe(CN)6]4- ions in the aqueous solution.

Earth's atmosphere is richest in :
  • a)
    ultraviolet
  • b)
    infrared
  • c)
    X-rays
  • d)
    microwaves
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
The correct answer is Option B. 
Earth 's atmosphere is richest in infrared radiation or IR.
* The earth emits huge amounts of infrared radiation and thereby makes the atmosphere richest in infrared rays.
* When sunlight (solar radiation) hits the earth, some of the energy is absorbed by the earth that ultimately heats up the earth.
* This heat gets radiated by the earth in the form of infrared radiation.
 

A magnetic moment of 1.73 BM will be shown by one among the following
  • a)
    [Cu(NH3)4]2+
  • b)
    [Ni(CN)4]2–
  • c)
    TiCl4
  • d)
    [CoCl6]4–
Correct answer is option 'A'. Can you explain this answer?

Ritu Singh answered
The correct answer is Option A.
Electronic configuration of Cu2+  ion in [Cu(NH3)4]2+.
Cu2+ ion =[Ar]3d94s0.
∴Cu2+ ion has one unpaired electron.
Magnetic moment of [Cu(NH3)4]2+ (μ) = BM
where, n = no. of unpaired electrons

Whereas Ni2+ in [Ni(CN)4]2− , Ti4+ in TiCl4 and Co2+ ion [COCl6]4− has 2,0 and 3 unpaired electrons respectively.

The spin only magnetic moment value (in Bohr magneton units) of Cr(CO)6 is
  • a)
    0
  • b)
    2.84
  • c)
    4.90
  • d)
    5.92
Correct answer is option 'A'. Can you explain this answer?

Rahul Bansal answered
The electron configuration is [Ar]3d^5 4s^1.We have to accomodate the 6 Ligands and the fact that CO is a strong ligand.
This results in d^2sp^3 hybridization. Therefore, there are no unpaired electrons in Cr(CO)6. Hence n=0
And the spin only magnetic moment is also 0.

The effective atomic number of Fe in Fe(CO)5 is
  • a)
    36
  • b)
    24
  • c)
    34
  • d)
    26
Correct answer is option 'A'. Can you explain this answer?

Anupama Nair answered
EAN= atomic no of Fe - oxidation state + no of e donated by ligand... Oxidation state of Fe is 0 since CO is neutral ligand... Two donor atoms hence no of e = 2×5=10.... EAN= 26-0+10=36

The formula of the complex hexamminecobalt (III) chloride sulphate is
  • a)
    [Co(NH3)6]CISO4
  • b)
    [Co(NH3)6CI]SO4
  • c)
    [Co(NH3)6CISO4]
  • d)
    None of these
Correct answer is 'A'. Can you explain this answer?

Anshika Menon answered
Formula of Complex Hexamminecobalt (III) Chloride Sulphate

The correct answer is 'A' which represents the formula [Co(NH3)6]ClSO4. Let's break down the answer into the following headings:

I. Understanding the Formula
II. Explanation of the Formula
III. Conclusion

I. Understanding the Formula
Before we dive into the formula, let's understand some key terms:
- Complex: A molecule or ion formed by the combination of a metal ion with a ligand (a molecule or ion that can donate a pair of electrons to the metal ion)
- Hexamminecobalt (III) chloride: A complex formed by the combination of cobalt (III) ion with six ammonia molecules and one chloride ion
- Sulphate: A compound containing the sulphate ion (SO4 2-)

II. Explanation of the Formula
The given complex contains cobalt (III) ion, six ammonia molecules (NH3), one chloride ion (Cl-), and one sulphate ion (SO4 2-). The cobalt (III) ion is coordinated by six ammonia molecules forming an octahedral complex. The chloride ion and sulphate ion occupy the remaining two positions of the octahedral complex. Therefore, the formula of the complex is [Co(NH3)6]ClSO4.

III. Conclusion
In conclusion, the formula of the complex hexamminecobalt (III) chloride sulphate is [Co(NH3)6]ClSO4. The complex contains cobalt (III) ion coordinated by six ammonia molecules, one chloride ion, and one sulphate ion.

Which of the following statements is/are correct?
  • a)
    [Co(en)2NO2Cl] Br is cationic complex
  • b)
    [Co(en)3]CI3 produces 3 ions in solution
  • c)
    [Fe(CO)5] is neutral complex
  • d)
    [Cu(NH3)4]SO4 is deep blue colour
Correct answer is option 'A,C,D'. Can you explain this answer?

Nikita Singh answered
[Co(en)3]CI3 produces 4 ions in solution as follows :
[Co(en)3] CI3→ [Co(en)3]3+ + 3CI-
 
  1. is correct as charge on the complex ion will be +1
  2.  is incorrect as the complex will form 4 ions in solution
  3. is correct as there is no charge on the complex
  4. is also correct as cu+2 has blue color in solution
Hence A, C and D are correct.

The hybrisation of Co in [Co(H2O)6]3+ is :
  • a)
    d2sp3
  • b)
    dsp2
  • c)
    dsp3
  • d)
    spd3
Correct answer is option 'A'. Can you explain this answer?

Rajeev Saxena answered
In this complex compound the total charge is +3 as H2O is a neutral compound so the oxidation state of cobalt is +3 and the electronic configuration of Co is 3d7 4s2. So, Co(+3)=4d6 and H2O is a weak ligand so there is no pairing of electron. So,4s 4p3 and 4d2 orbital make hybrid orbital to have a hybridization of d2sp3.

Complex compounds are addition compounds formed by the stoichiometric combination of two or more simple salts but do not decompose into constituent ions completely. The first such complex prepared by Tassaert is hexamine cobalt (III) chloride. Later many such compounds were prepared and their properties were studied. The chloramines complexes of cobalt (III) chromium (III) not only exhibit a spectrum of colours but also differ in the reactivity of their chlorides. Moreover, greater the number of ions produced by a complex in solution, greater is the electrical conductivity. This type of information was obtained for several series of complexes.
Q. 
The number of ions per mole of the complex CoCI3 . 5NH3 in aqueous solution will be
  • a)
    3
  • b)
    9
  • c)
    2
  • d)
    4
Correct answer is option 'A'. Can you explain this answer?

Suresh Iyer answered
[Co(NH3)5CI]CI2→[Co(NH3)5CI]2++ 2Cl- 
Hence, 3 ions are present for one mole of the complex in the solution.

Which of the following complex ion is not expected to absorb visible light ? [2010]
  • a)
    Ni(CN)42
  • b)
    Cr(NH3)6 3
  • c)
    2Fe(H2 O)6
  • d)
    Ni(H2O)62
Correct answer is option 'A'. Can you explain this answer?

Mahesh Saini answered
Absorption of visual light is associated with an energy difference between two orbitals — one occupied, one unoccupied — and electrons must be able to be excited from one to the other.

In coordination complexes, these excitations typically happen within the metal’s d subshell, so it is usually sufficient to examine that and approximately determine which excitations are possible. The main selection rules are:

the spin rule. The electron must be excitable without a spin-flip
the Laporte rule. Basically, d to d transitions are forbidden in octahedral complexes
The spin rule is very strongly observed. The color of manganese(II) whose transition is spin-forbidden is extremely faint. The Laporte rule only holds true as long as the complex is inversion-symmetric, so any asymmetric vibration is enough to make it void; thus, Laporte-forbidden transitions are typically still visible but somewhat faint.

Let’s examine the complexes:

[Ni(CN)4]2−This is expected to be square planar and d8. The energy difference between the two highest orbitals — dxy and dx2−y2 — is expected to be high. The former is expected to be fully populated, the latter to be unpopulated.
[Cr(NH3)6]3+ This is a d3 system. It is expected to be octahedral with a standard difference between the lower and higher energy levels.
[Fe(H2O)6]2+This is a d6 octahedral system. There is no reason to assume a low spin state. The energy difference is expected to be slightly less than in the previous case.
[Ni(H2O)6]2+ this is expected to be a high-spin d8system and octahedral. The same expectation regarding energy levels as on the previous case applies.
We realize that the of our complexes are average high spin octahedral complexes. For these, visible light absorption is always expected. Only one case is different. In that different case, the HOMO-LUMO difference is large. While we can still expect absorption, it seems most reasonable to assign this absorption band an ultraviolet wavelength.

Thus, [Ni(CN)4]2− is the answer.

The complex potassium dicyanodioxalatonickelate (II) in solution produce....... ions.
    Correct answer is '5'. Can you explain this answer?

    Anaya Patel answered
    The structure of potassium dicyanodio xalatonickelate (II) is
    K4[Ni(CN)2(ox)2].
    K4[Ni(CN)2(ox)2] →  4K+ + [Ni(CN)2(ox)2]- 
    This produce 5 ions in solution.

    Number of EDTA molecules required to form an octahedral complex.
      Correct answer is '1'. Can you explain this answer?

      Mira Sharma answered
      One EDTA (ethylenediaminetetraacetic acid) molecule is required to make an octahedral complex with Ca^2+ ion

      When AgNO3 solution is added in excess to 1 M solution of CoCI3 . xNH3, one mole of AgCI is formed. The value of x is
        Correct answer is '4'. Can you explain this answer?

        Nikita Singh answered
        AgNO3 solution is added in excess of 1 M solution of CoCI3 . xNH3.
        CoCl3​.xNH3​+AgNO3​→AgCl (1mole)
        This precipitation of 1 mol of AgCl by this reaction shows that there is only one Cl outside the coordination sphere, which is not as a ligand ( as ligands are not ionisable).
        Hence, the compound must be as follows:(showing the coordination sphere) [Co(NH3​)4​Cl2​]Cl, as this is the octahedral complex, where it is clear that there are only 2 Cl as ligand and other ligands are NH3​. 
        So, 6−2 = 4 NH3​ ligands.

        Only One Option Correct Type
        Direction (Q. Nos. 1-10) This section contains 10 multiple choice questions. Each question has four choices (a), (b), (c) and (d), out of which ONLY ONE is correct.
        Q. 
        Primary and secondary valency of Pt in [Pt(en)2CI2] are
        • a)
          + 4 and - 4
        • b)
          + 4 and 6
        • c)
          + 6 and 4
        • d)
          + 2 and 6
        Correct answer is option 'D'. Can you explain this answer?

        Rahul Bansal answered
        The primary valence is its oxidation number, which is +2 in this case (en is uncharged, and the Cl ligands carry a -1 charge each, so Pt must be +2 to balance).
        Secondary valence is coordination number. The en ligand is bidentate, and Cl is monodentate, so you have 2(2) + 2(1) = 6, so the Pt has a coordination number of 6.

        In the formation of complex entity, the central atom/ion acts as
        • a)
          Bronsted acid
        • b)
          Lewis base
        • c)
          Lewis acid
        • d)
          Bronsted base
        Correct answer is option 'C'. Can you explain this answer?

        Arka Das answered
        Explanation:

        In the formation of a complex entity, a central atom/ion acts as a Lewis acid. This can be explained as follows:

        Lewis Acid and Lewis Base:
        According to Lewis acid-base theory, a Lewis acid is a species that accepts a pair of electrons to form a coordinate covalent bond, while a Lewis base is a species that donates a pair of electrons to form a coordinate covalent bond.

        Formation of Complex Entity:
        A complex entity is formed by the coordination of a central atom/ion with one or more ligands. Ligands are molecules or ions that donate a pair of electrons to the central atom/ion to form a coordinate covalent bond.

        Role of Central Atom/Ion:
        In the formation of a complex entity, the central atom/ion acts as a Lewis acid because it accepts a pair of electrons from the ligands to form a coordinate covalent bond. The central atom/ion has an incomplete outer shell, which makes it electron deficient and thus able to accept electrons from other species.

        Examples:
        Some examples of complex entities and their central atom/ion are as follows:

        - In [Fe(CN)6]4-, Fe2+ acts as the central ion, which accepts electrons from the CN- ligands.
        - In [Cu(NH3)4]2+, Cu2+ acts as the central ion, which accepts electrons from the NH3 ligands.
        - In [Ag(NH3)2]+, Ag+ acts as the central ion, which accepts electrons from the NH3 ligands.

        Conclusion:
        Thus, we can conclude that in the formation of a complex entity, the central atom/ion acts as a Lewis acid because it accepts a pair of electrons from the ligands to form a coordinate covalent bond.

        Which is the diamagnetic?
        • a)
          [CoF6]3-
        • b)
          [Ni(CN)4]2-
        • c)
          [NiCI3]2-
        • d)
          [Fe(CN)6]3-
        Correct answer is option 'B'. Can you explain this answer?

        Niti Mishra answered
        Explanation:

        Diamagnetic substances are those which do not have any unpaired electrons and are not attracted by a magnetic field. On the other hand, paramagnetic substances have unpaired electrons and are attracted by a magnetic field.

        Let's examine the given options to determine which one is diamagnetic.

        [CoF6]3-
        Cobalt has 27 electrons. In this complex, cobalt is in the +3 oxidation state. The six fluoride ions act as ligands and each donate one pair of electrons to the cobalt ion. The complex has a total of 33 electrons, and there are three unpaired electrons in the d-orbitals of the cobalt ion. Therefore, [CoF6]3- is a paramagnetic complex.

        [Ni(CN)4]2-
        Nickel has 28 electrons. In this complex, nickel is in the +2 oxidation state. The four cyanide ions act as ligands and each donate one pair of electrons to the nickel ion. The complex has a total of 34 electrons, and all the electrons are paired. Therefore, [Ni(CN)4]2- is a diamagnetic complex.

        [NiCl4]2-
        Similar to the above complex, nickel has 28 electrons and is in the +2 oxidation state. The four chloride ions act as ligands and each donate one pair of electrons to the nickel ion. The complex has a total of 32 electrons, and all the electrons are paired. Therefore, [NiCl4]2- is a diamagnetic complex.

        [Fe(CN)6]3-
        Iron has 26 electrons. In this complex, iron is in the +3 oxidation state. The six cyanide ions act as ligands and each donate one pair of electrons to the iron ion. The complex has a total of 32 electrons, and there are five unpaired electrons in the d-orbitals of the iron ion. Therefore, [Fe(CN)6]3- is a paramagnetic complex.

        Therefore, the diamagnetic complex among the given options is [Ni(CN)4]2-.

        Can you explain the answer of this question below:

        sp3-hybridisation is found in

        • A:

          [ZnCI4]2-

        • B:

          [Cu(NH3)4]2+

        • C:

          [CuCI4]2-

        • D:

          [Ni(CO)4]

        The answer is A,C,D.

        Dipika Rane answered
        Explanation:

        SP3 hybridization is a type of hybridization where one s orbital and three p orbitals of the same shell of an atom mix to form four sp3 hybrid orbitals. These hybrid orbitals are arranged in a tetrahedral shape around the central atom.

        The given options are:

        a) [ZnCl4]2-
        b) [Cu(NH3)4]2
        c) [CuCl4]2-
        d) [Ni(CO)4]

        a) [ZnCl4]2-: In this complex ion, the central zinc atom is sp3 hybridized. The zinc ion has an electronic configuration of [Ar]3d104s0. The hybridization of the zinc ion takes place by mixing one 4s orbital and three 4p orbitals to form four sp3 hybrid orbitals.

        b) [Cu(NH3)4]2: In this complex ion, the central copper atom is dsp2 hybridized. The copper ion has an electronic configuration of [Ar]3d104s1. The hybridization of the copper ion takes place by mixing one 4s orbital, two 4p orbitals, and one 3d orbital to form five dsp2 hybrid orbitals.

        c) [CuCl4]2-: In this complex ion, the central copper atom is sp3 hybridized. The copper ion has an electronic configuration of [Ar]3d104s1. The hybridization of the copper ion takes place by mixing one 4s orbital and three 4p orbitals to form four sp3 hybrid orbitals.

        d) [Ni(CO)4]: In this complex ion, the central nickel atom is sp3 hybridized. The nickel ion has an electronic configuration of [Ar]3d84s2. The hybridization of the nickel ion takes place by mixing one 4s orbital and three 4p orbitals to form four sp3 hybrid orbitals.

        Conclusion:

        Thus, the correct options are A, C, and D, as all these complex ions have a central atom that is sp3 hybridized. The complex ion in option B has a central copper atom that is dsp2 hybridized.

        Statement Type
        Direction (Q. Nos. 24 and 25) This section is based on Statement I and Statement II. Select the correct answer from the codes given below.
        Q. 
        Statement I : Oxidation state of Fe in Fe(CO)5 is zero.
        Statement II : EAN of Fe in this complex is 36.
        • a)
          Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I
        • b)
          Both Statement I and Statement II are correct but Statement II is not the correct explanation of Statement I
        • c)
          Statement I is correct but Statement II is incorrect
        • d)
          Statement II is correct but Statement I is incorrect
        Correct answer is option 'B'. Can you explain this answer?

        Shail Chakraborty answered
        Statement I is true because CO is a neutral ligand, Statement II is true because
        EAN of Fe
        = Atomic number of Fe + Electrons gained by coordination
        = 26 + 2 x 5 = 36
        But Statement II is not the correct explanation. Correct explanation is that oxidation state of Fe in Fe(CO)5 is zero because CO is a neutral ligand.

        Chapter doubts & questions for Coordination Compounds - Topic-wise MCQ Tests for NEET 2025 is part of NEET exam preparation. The chapters have been prepared according to the NEET exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for NEET 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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