Haemoglobin is a naturally occurring complex in which the central metal ion is
Correct answer: B. iron
- A. magnesium
- B. iron
- C. cobalt
- D. copper
Explanation
Each haem group holds an iron two ion coordinated to four nitrogen atoms of the porphyrin ring, with the remaining site available to bind oxygen reversibly. Magnesium is the central ion of chlorophyll and cobalt that of vitamin B12, both of which are offered here as the parallel biological cases. Carbon monoxide is toxic because it binds the same iron site far more strongly than oxygen.
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About Electronic Structure of d-Block Elements
The electronic structure of d-block elements covers the filling of the (n-1)d and ns orbitals, general electronic configurations, and the exceptions shown by chromium and copper. It explains how partially filled d orbitals produce variable oxidation states, coloured ions, magnetic behaviour and complex formation, while distinguishing transition elements from elements with completely filled d subshells.
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