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Atomic number of Cr and Fe are respectiv...

Atomic number of Cr and Fe are respectively 24 and 26, which of the following is paramagnetic with the spin of electron : -

A

`[Cr(CO)_6]`

B

`[Fe(CO)_5]`

C

`[Fe(CN)_6]^(-4)`

D

`[Cr(NH_3)_6]^(+3)`

Text Solution

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The correct Answer is:
To determine which of the given compounds is paramagnetic with respect to the spin of electrons, we need to analyze the electronic configurations of chromium (Cr) and iron (Fe) in their respective oxidation states when they form complexes. ### Step-by-Step Solution: 1. **Identify the Atomic Numbers**: - Chromium (Cr) has an atomic number of 24. - Iron (Fe) has an atomic number of 26. 2. **Determine the Electronic Configurations**: - The electronic configuration of Cr (in the ground state) is: \[ \text{Cr: } [Ar] 4s^1 3d^5 \] - The electronic configuration of Fe (in the ground state) is: \[ \text{Fe: } [Ar] 4s^2 3d^6 \] 3. **Analyze the Compounds**: - **Compound A: Chromium Carbonyl (Cr(CO)₆)**: - Oxidation state of Cr = 0. - Configuration remains: \(4s^1 3d^5\). - CO is a strong field ligand, causing pairing of electrons. Thus, it becomes diamagnetic (no unpaired electrons). - **Compound B: Iron Carbonyl (Fe(CO)₆)**: - Oxidation state of Fe = 0. - Configuration remains: \(4s^2 3d^6\). - CO is a strong field ligand, causing pairing of electrons. Thus, it becomes diamagnetic (no unpaired electrons). - **Compound C: Iron Cyanide (Fe(CN)₆)²⁻**: - Oxidation state of Fe = +2. - Configuration for Fe²⁺: \(4s^0 3d^6\). - CN⁻ is a strong field ligand, causing pairing of electrons. Thus, it becomes diamagnetic (no unpaired electrons). - **Compound D: Chromium Ammonia Complex (Cr(NH₃)₆)³⁺**: - Oxidation state of Cr = +3. - Configuration for Cr³⁺: \(4s^0 3d^3\). - NH₃ is a weak field ligand, but in this case, there are three unpaired electrons in \(3d^3\). Thus, it is paramagnetic. 4. **Conclusion**: - The compound that is paramagnetic is **Compound D: Cr(NH₃)₆³⁺** with three unpaired electrons. ### Final Answer: The correct answer is **Compound D: Cr(NH₃)₆³⁺**, which is paramagnetic with three unpaired electrons.
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