Which of the following has maximum unpaired d-electrons ?

To determine which of the given ions has the maximum number of unpaired d-electrons, let’s examine their electron configurations. Here’s how we can approach it:

• Zn⁺:
  Neutral Zn is [Ar] 3d¹⁰ 4s².
  Removing one electron gives Zn⁺: [Ar] 3d¹⁰.
  All d-electrons are paired, so unpaired = 0.
• Fe²⁺:
  Neutral Fe is [Ar] 3d⁶ 4s².
  Removing two electrons gives Fe²⁺: [Ar] 3d⁶.
  For d⁶, the typical configuration is t₂g⁴e_g², resulting in 4 unpaired electrons.
• Ni³⁺:
  Neutral Ni is [Ar] 3d⁸ 4s².
  Removing three electrons gives Ni³⁺: [Ar] 3d⁷.
  For d⁷, the configuration is t₂g⁵e_g², resulting in 3 unpaired electrons.
• Cu⁺:
  Neutral Cu is [Ar] 3d¹⁰ 4s¹.
  Removing one electron gives Cu⁺: [Ar] 3d¹⁰.
  All d-electrons are paired, so unpaired = 0.

Answer:
Fe²⁺ has the maximum number of unpaired d-electrons (4).