Find the relation between the first two words and choose the word that has the same relationship with the third word, from the alternatives.
Haemoglobin : Iron :: Chlorophyll : ?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Magnesium
The pair is a pigment and the metal atom at its centre. Haemoglobin, the red pigment of blood that carries oxygen, has an iron atom at the centre of each of its haem groups. Chlorophyll, the green pigment of plants that traps light for photosynthesis, has a magnesium atom at its centre in the same way.
Why the other options are incorrect
Option (1) Copper — Incorrect. Copper is the metal of haemocyanin, the blue oxygen-carrying pigment of snails, octopuses and crabs.
Option (3) Cobalt — Incorrect. Cobalt is the metal at the centre of vitamin B12 (cobalamin).
Option (4) Calcium — Incorrect. Calcium is the main mineral of bones and teeth, not part of any pigment.