Answer: Magnesium (Mg 2+ at the porphyrin centre).
- A Magnesium (Mg<sup>2+</sup> at the porphyrin centre)
- B Calcium, coordinated at the centre of the porphyrin ring
- C Sodium, held loosely at the centre of the porphyrin structure
- D Barium, chelated within the porphyrin macrocycle
Correct answer: A. Magnesium (Mg<sup>2+</sup> at the porphyrin centre)
Explanation: Chlorophyll has a porphyrin ring with Mg<sup>2+</sup> at its centre, essential for light absorption in photosynthesis.
Each s-block metal ion emits a characteristic flame colour because heating excites electrons to higher energy levels; light is emitted as they fall back, with the colour determined by the specific energy gap.
Concept context
Group 1 (alkali metals) and Group 2 (alkaline earth metals). Learn their reactions with water and air, important compounds like NaOH, Na₂CO₃, and CaCO₃, and anomalous behaviour of lithium and beryllium.