Which transition metal is known for its multiple colorful oxidation states and compounds used in pigments and paints?

Analysis of the Question

The question asks for a transition metal characterized by its ability to exhibit multiple oxidation states, which result in a variety of vibrant colors. These compounds are widely utilized in the manufacturing of pigments and paints.

Concept Explanation

Transition metals are defined by their ability to form stable ions with partially filled d-orbitals. This electronic structure allows them to:

1. Exhibit variable oxidation states: Because the energy difference between the $ns$ and $(n-1)d$ orbitals is small, electrons can be lost easily in different combinations.
2. Form colored compounds: When transition metal ions form complexes, the d-orbitals split into different energy levels. Electrons can absorb specific wavelengths of visible light to jump between these levels (d-d transitions), causing the compounds to appear colored.

While many transition metals exhibit these properties, Copper (Cu) is historically and industrially famous for its distinct, vibrant colors (like the deep blue of copper(II) sulfate or the bright green of copper carbonates) used extensively in pigments, dyes, and paints.

Step-by-Step Evaluation

• A. Silver (Ag): Primarily exhibits a +1 oxidation state. Its compounds are mostly colorless or white, except for specific halides used in photography.
• B. Copper (Cu): Exhibits +1 and +2 oxidation states. Its compounds are famously colorful (blues and greens) and have been used for centuries in pigments (e.g., Verdigris, Azurite).
• C. Gold (Au): Primarily exhibits +1 and +3 states. While it forms colored compounds, it is not the primary metal associated with common industrial pigments compared to copper.
• D. Zinc (Zn): While a d-block element, it is not a "true" transition metal because it has a full $d^{10}$ configuration in its common +2 state. Consequently, its compounds are typically white or colorless, not colorful.

Conclusion

Based on the chemical properties of transition metals and their industrial application in pigments, Copper is the most accurate answer.

Exam Tip

When you see questions about "colorful compounds" in transition metals, always look for elements like Copper (Cu), Iron (Fe), Chromium (Cr), or Manganese (Mn). If you see Zinc (Zn) or Scandium (Sc), remember they are often "exceptions" that do not form colored compounds because they lack partially filled d-orbitals in their common oxidation states!