Match the entries of column I with appropriate entries of column II and choose the correct option out of the four options given.

(a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

The correct answer is option  4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii).

Let us delve deeper into each pairing:

(a) Chlorophyll - (iv) Magnesium:

Chlorophyll is a vital pigment found in plants and other photosynthetic organisms. Its primary function is to absorb light energy during photosynthesis, which is then used to convert carbon dioxide and water into glucose and oxygen. The central atom in the chlorophyll molecule is magnesium \((Mg)\), which is coordinated to a porphyrin ring structure. This coordination allows magnesium to play a crucial role in capturing light energy and transferring it to the photosynthetic reaction center, where the conversion of light energy into chemical energy takes place. Without magnesium, chlorophyll cannot effectively absorb light and carry out photosynthesis, making it essential for plant growth and survival.

(b) Blood pigment - (iii) Iron:

Blood pigment refers to the proteins responsible for transporting oxygen throughout the body. Two prominent examples are hemoglobin, found in red blood cells, and myoglobin, found in muscle cells. Both hemoglobin and myoglobin contain a central metal atom, which is iron \((Fe)\). In these proteins, iron is coordinated to a porphyrin ring structure known as heme. The iron atom within the heme group can reversibly bind oxygen molecules, allowing for efficient oxygen transport from the lungs to tissues and organs throughout the body. Additionally, iron plays a crucial role in the regulation of oxygen affinity, ensuring that oxygen is released to tissues when needed, such as during physical activity.

(c) Wilkinson catalyst - (i) Rhodium:

The Wilkinson catalyst, named after chemist Geoffrey Wilkinson, is a well-known homogeneous catalyst used in organic synthesis. It consists of a transition metal complex featuring rhodium \((Rh)\) as the central metal atom. Specifically, the Wilkinson catalyst is represented as \([RhCl(PPh_3)_3]\), where \(PPh_3\) represents a triphenylphosphine ligand. This complex is widely used in various organic transformations, including hydrogenation reactions, where it facilitates the addition of hydrogen to unsaturated organic compounds. The rhodium center in the Wilkinson catalyst acts as a site for coordinating reactant molecules and facilitating the catalytic process, leading to increased reaction rates and selectivity in organic synthesis.

(d) Vitamin \(B_{12}\) - (ii) Cobalt:

Vitamin \(B_{12}\), also known as cobalamin, is an essential micronutrient required for various metabolic processes in the human body. It plays a critical role in DNA synthesis, nerve function, and the metabolism of amino acids and fatty acids. The central atom in the vitamin \(B_{12}\) molecule is cobalt \((Co)\), which is coordinated to a corrin ring structure. Cobalt forms a complex with the corrin ring, creating the core structure of the vitamin \(B_{12}\) molecule. This complex structure allows vitamin \(B_{12}\) to serve as a cofactor for enzymes involved in key metabolic pathways, such as methionine synthesis and the conversion of methylmalonyl-CoA to succinyl-CoA. Without cobalt, vitamin \(B_{12}\) cannot fulfill its biological functions, leading to deficiencies that can result in various health problems, including anemia and neurological disorders.

In summary, each pairing represents a specific coordination compound with its corresponding central metal atom, showcasing the diverse roles of transition metals in biological systems and chemical catalysis. These examples highlight the importance of coordination chemistry in understanding the structures and functions of complex molecules in nature and synthetic applications.