NDA General Ability Question (2025) — Solution

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Nitrogen dioxide (NO_2) is an odd-electron molecule containing 17 valence electrons. Due to the presence of an unpaired electron on the nitrogen atom, it is highly reactive and paramagnetic. To achieve stability by pairing the odd electron, NO_2 undergoes dimerization to form dinitrogen tetroxide (N_2O_4), which is a diamagnetic and even-electron molecule. 2NO_2 N_2O_4 The other oxides (N_2O, N_2O_3, N_2O_5) are even-electron molecules and do not dimerize. Answer: NO_2