Which of the following statements is incorrect?

The correct answer is Option (2) → Chlorophyll, the green pigment of plants, is a coordination compound of cobalt.

Chlorophyll, the pigment responsible for photosynthesis, is a coordination compound of magnesium, not cobalt. The biologically important coordination compound of cobalt is vitamin B₁₂.

Option (1) Haemoglobin, the red pigment of blood, is a coordination compound of iron and acts as an oxygen carrier. — A correct statement. Haemoglobin is an iron complex that carries oxygen in the blood.

Option (2) Chlorophyll, the green pigment of plants, is a coordination compound of cobalt. — An incorrect statement. The central metal of chlorophyll is magnesium.

Option (3) The enzymes carboxypeptidase A and carbonic anhydrase contain coordinated metal ions. — A correct statement. These enzymes, the catalysts of biological systems, are compounds with coordinated metal ions.

Option (4) Impure nickel is purified by converting it to [Ni(CO)₄], which is then decomposed to give pure nickel. — A correct statement. The complex \( \ce{[Ni(CO)4]} \) is formed from impure nickel and then decomposed to yield pure nickel.

NCERT (2026-27 edition):
5.7 Importance and Applications of Coordination Compounds – “… The pigment responsible for photosynthesis, chlorophyll, is a coordination compound of magnesium.”