Q7 / 100 · BITSAT 2024 (Memory Based Paper 3) · Chemistry

Electron affinity is positive, when

  • A
    O changes into $\mathrm{O}^{-}$
  • Correct answer
    B
    $\mathrm{O}^{-}$changes to $\mathrm{O}^{2-}$
  • C
    O changes into $\mathrm{O}^{+}$
  • D
    O changes to $\mathrm{O}^{2+}$

Solution

When $\mathrm{O}^{-}$changes into $\mathrm{O}^{2-}$, energy is absorbed i.e the change is endothermic because $\mathrm{O}^{-}$repels the incoming electron due to similar charge. H ice, it needs energy to add (accept) the electron. So, electron affinity $\left(\mathrm{EA}_2\right)$ is positive.

Hence, the correct answer is option: 'B'.

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