Question

In following pairs, the one in which both transition metal ions are colourless is :

• A. Sc³⁺, Zn²⁺
• B. Ti⁴⁺, Cu²⁺
• C. V²⁺, Ti³⁺
• D. Zn²⁺, Mn²⁺

Answer 1

The Correct Option is A

To determine which pair of transition metal ions is colourless, we need to understand the concept of colour in transition metals. The colour in transition metal ions is primarily due to the electronic transitions between the d-orbitals. Here, we will analyze each pair to identify if they're colourless:v

• Sc³⁺ and Zn²⁺:
  • Sc³⁺: Scandium ion Sc³⁺ has an empty d-subshell (d⁰ configuration) as all three electrons are removed upon forming the ion. No d-d transitions can occur, thus making it colourless.
  • Zn²⁺: Zinc ion Zn²⁺ has a completely filled d-subshell with an electronic configuration of [Ar]3d¹⁰. It does not allow d-d transitions, which implies it is also colourless.
• Ti⁴⁺ and Cu²⁺:
  • Ti⁴⁺: Similar to Sc³⁺, Ti⁴⁺ has a d⁰ configuration, which makes it colourless.
  • Cu²⁺: Copper ion Cu²⁺ has a d⁹ configuration, which supports d-d transitions, making it coloured.
• V²⁺ and Ti³⁺:
  • V²⁺: Vanadium ion V²⁺ has a d³ configuration that allows d-d transitions, implying it is coloured.
  • Ti³⁺: Titanium ion Ti³⁺ has a d¹ configuration, allowing for d-d transitions and therefore is coloured.
• Zn²⁺ and Mn²⁺:
  • Zn²⁺: As mentioned earlier, Zn²⁺ is colourless due to the fully filled d-subshell.
  • Mn²⁺: Manganese ion Mn²⁺ has a d⁵ configuration. It allows electronic transitions within partly filled d-orbitals, making it coloured.

Based on the above analysis, the pair Sc³⁺ and Zn²⁺ is the only one where both ions are colourless. This is due to the absence of d-d transitions in Sc³⁺ and the fully filled 3d-subshell of Zn²⁺.

Answer 2

Scandium ions (Sc⁺³) and zinc ions (Zn⁺²) are colorless due to the absence of unpaired electrons. In contrast, transition metal ions such as copper ions (Cu⁺²), titanium ions (Ti⁺³), vanadium ions (V⁺²), and manganese ions (Mn⁺²) exhibit color as they possess unpaired electrons.
When these transition metal ions absorb light in the visible region, an unpaired electron from a lower energy d orbital is excited to a higher energy d orbital. The observed color is complementary to the absorbed light frequency.
So, the correct option is (A): Sc³⁺, Zn²⁺