Medium MCQ +4 / -1 PYQ · JEE Mains 2025

The number of unpaired electrons responsible for the paramagnetic nature of the following complex species are respectively :

[Fe(CN)6]3−, [FeF6]3−, [CoF6]3−, [Mn(CN)6]3−

  1. A <p>1, 5, 4, 2</p> Correct answer
  2. B <p>1, 4, 4, 2</p>
  3. C <p>1, 5, 5, 2</p>
  4. D <p>1, 1, 4, 2</p>

Solution

<p>The number of unpaired electrons responsible for the paramagnetic nature of each complex species is calculated as follows:</p> <p><strong>Complex</strong>: $[Fe(CN)_6]^{3-}$ </p> <p><p><strong>Ion</strong>: $Fe^{3+}$</p></p> <p><p><strong>Electronic Configuration</strong>: $3d^5$</p></p> <p><p><strong>Orbital Population</strong>: </p> <p><p>$t_{2g}^{2,2,1}$</p></p> <p><p>$e_g^{0,0}$</p></p></p> <p><p><strong>Unpaired Electrons</strong>: 1</p></p> <p><strong>Complex</strong>: $[FeF_6]^{3-}$ </p> <p><p><strong>Ion</strong>: $Fe^{3+}$</p></p> <p><p><strong>Electronic Configuration</strong>: $3d^5$</p></p> <p><p><strong>Orbital Population</strong>: </p> <p><p>$t_{2g}^{1,1,1}$</p></p> <p><p>$e_g^{1,1}$</p></p></p> <p><p><strong>Unpaired Electrons</strong>: 5</p></p> <p><strong>Complex</strong>: $[CoF_6]^{3-}$ </p> <p><p><strong>Ion</strong>: $Co^{3+}$</p></p> <p><p><strong>Electronic Configuration</strong>: $3d^6$</p></p> <p><p><strong>Orbital Population</strong>: </p> <p><p>$t_{2g}^{2,1,1}$</p></p> <p><p>$e_g^{1,0}$</p></p></p> <p><p><strong>Unpaired Electrons</strong>: 4</p></p> <p><strong>Complex</strong>: $[Mn(CN)_6]^{3-}$ </p> <p><p><strong>Ion</strong>: $Mn^{3+}$</p></p> <p><p><strong>Electronic Configuration</strong>: $3d^4$</p></p> <p><p><strong>Orbital Population</strong>: </p> <p><p>$t_{2g}^{2,1,1}$</p></p> <p><p>$e_g^{0,0}$</p></p></p> <p><p><strong>Unpaired Electrons</strong>: 2</p></p> <p>Each complex's paramagnetic nature is due to the specific number of unpaired electrons as indicated above.</p>

About this question

Subject: Chemistry · Chapter: Coordination Compounds · Topic: Ligands and Coordination Number

This question is part of PrepWiser's free JEE Main question bank. 173 more solved questions on Coordination Compounds are available — start with the harder ones if your accuracy is >70%.

Drill 25 more like these. Every day. Free.

PrepWiser turns these solved questions into a daily practice loop. Chapter-wise drills, full mocks, AI doubt chat. No auto-renew.

Start free →