The formation of the oxide ion O2-(g) requires first an exothermic and then an endothermic step as shown below : O(g) + e- - O-(g); \Delta H = -142 kJ mol-1 and O-(g) + e- - O2-(g); \Delta H = 844 k

Question

The formation of the oxide ion O2-(g) requires first an exothermic and then an endothermic step as shown below : O(g) + e- -> O-(g); \Delta H = -142 kJ mol-1 and O-(g) + e- -> O2-(g); \Delta H = 844 kJ mol-1. This is because :

Prashant Kotian · Accepted Answer

Correct answer: C. Step 1: Note that Li+, Be2+, and B3+ are isoelectronic species, each possessing exactly 2 electrons. Step 2: For isoelectronic species, the ionic radius decreases as the atomic number (nuclear charge) increases, because a stronger nucleus pulls the same number of electrons more tightly. Step 3: The atomic numbers are Li (3), Be (4), and B (5). Therefore, the size order is Li+ > Be2+ > B3+, matching option (d).

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