Read the passage carefully and answer the questions.

The coordination compounds are of great importance. These compounds are widely present in the mineral, plants and animal world and are known to play many important functions in the area of analytical chemistry, metallurgy, biological systems, industry and medicine. For example, coordination compounds find use in many qualitative and quantitative chemical analysis. Some important metal extraction and purification make use of complex formation. Hardness of water can be estimated by stable complex formation of $ \text{Ca}^{2+}$ and $\text{Mg}^{2+} $

Impure nickel is converted to which of its complex to be decomposed to yield pure nickel?

$ [\text{Ni}(\text{CO})_4] $

The correct answer is Option (2) → $ [\text{Ni}(\text{CO})_4] $

Impure nickel is treated in a stream carbon monoxide to form a volatile complex:

$ \text{Ni}+4\text{CO}\rightarrow\text{Ni}(\text{CO})_4 $

This complex is then heated to a higher temperature (around $450\text{ K}$) where it decomposes to give pure nickel:

$ \text{Ni}(\text{CO})_4\rightarrow\text{Ni}(\text{pure})+4\text{CO} $

This is a real-world industrial purification process known as Mond Process, which uses the volatility of the metal carbonyl complex.