Question

The metal complex ion that is paramagnetic is ______.

(Atomic number of Fe = 26, Cu = 29, Co = 27 and Ni = 28)

Options

• [Fe(CN)₄]²⁻

• [Co(NH₃)₆]³⁺

• [Ni(CN₄)]²⁻

• [Cu(NH₃)₄]²⁺

Answer 1

The metal complex ion that is paramagnetic is [Cu(NH₃)₄]²⁺.

Explanation:

Paramagnetic substances have unpaired electrons, while diamagnetic substances have all electrons paired

1. [Fe(CN)₄]²⁻
   Assume x is the oxidation number of Fe in given complex.
   x + 4(−1) = −2
   x − 4 = − 2
   x = − 2 + 4
   = + 2
   Electronic configuration of Fe = [Ar]3d⁶4s²
   Fe⁺² = [Ar]3d⁶
   All electrons are paired; hence, it is diamagnetic in nature [Co(NH₃)₆]³⁺
   
2. Assume x is the oxidation number of Co in given complex.
   x + 6(0) = + 3
   x = + 3
   Electronic configuration of Co = [Ar] 3d⁷4s²
   Co⁺³ = [Ar]3d⁶
3. All electrons are paired; hence, it is diamagnetic [Ni(CN₄)]²⁻
   Assume x is the oxidation number of Ni in the given complex.
   x + 4(−1) =− 2
   x − 4 = − 2
   x = + 2
   Electronic configuration of Ni = [Ar] 3d⁸4s²
   Ni²⁺ = [Ar]3d⁸
4. All electrons are paired, hence, it is diamagnetic [Cu(NH₃)₄]²⁺.
   Assume x is the oxidation number of Cu in the given complex.
   x + 4(0) = + 2
   x = + 2
   Electronic configuration of Cu = [Ar] 3d¹⁰ 4s¹
   Cu⁻² = [Ar]3d⁹
   It has one unpaired electron; hence, it is paramagnetic.