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JEE Chemistry 2026 Question with Solution

The statements that are incorrect about the nickel(II) complex of dimethylglyoxime are :

A. It is red in colour.

B. It has a high solubility in water at pH = 99.

C. The Ni ion has two unpaired d-electrons.

D. The N – Ni – N bond angle is almost close to 90∘90^\circ.

E. The complex contains four five-membered metallacycles (metal containing rings).

Choose the correct answer from the options given below :

  • A

    C and E Only

  • B

    B, C and E Only

  • C

    A, D and B Only

  • D

    C and D Only

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: The statements are about the nickel(II) complex of dimethylglyoxime, i.e. Ni(DMG)2Ni(DMG)_2.

Find: Which statements are incorrect.

From the solution, Ni(DMG)2Ni(DMG)_2 is a square planar, neutral complex with a distinct red colour.

  1. Statement A: Correct. The complex is a rosy-red precipitate.
  2. Statement B: Incorrect. It is highly insoluble in water, which is why it is used for the gravimetric estimation of nickel.
  3. Statement C: Incorrect. As a square planar d8d^8 complex with strong field behavior from nitrogen donors, it is diamagnetic and has 00 unpaired electrons.
  4. Statement D: Correct. Square planar geometry implies bond angles close to 90∘90^\circ.
  5. Statement E: Incorrect. It contains two five-membered chelate rings (Ni-N-C-C-N)\left(\text{Ni-N-C-C-N}\right) and two six-membered rings formed by hydrogen bonding, not four five-membered metallacycles.

Therefore, the incorrect statements are B, C and E only. So, the correct option is B.

Common mistakes

  • Assuming the complex is soluble in water because it is used in analysis. This is wrong because its analytical use in gravimetric estimation depends on its insolubility. Check the physical basis of the test, not only the reagent name.

  • Treating the nickel complex as if it had unpaired electrons by default for Ni2+Ni^{2+}. This is wrong because geometry and ligand field matter; in square planar d8d^8 complexes, the complex is diamagnetic. Determine electron pairing after identifying the geometry.

  • Counting all rings in the structure as five-membered metallacycles. This is wrong because only the chelate rings containing nickel are metallacycles; the hydrogen-bonded rings are not five-membered metal-containing rings. Distinguish chelate rings from hydrogen-bonded rings.

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