The answer given for this question is 3, but according to me if asked for Hund's rule violation then it would be 1, as electrons are not distributed among the subshell in such a way to give maximum number of unpaired electron with parallel spin.
closed as unclear what you're asking by Mithoron, bon, Jan, airhuff, pentavalentcarbon Oct 22 '17 at 14:01
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The answer is 3 because according to Aufbau principle electrons are distributed according to energy levels that means S orbital should be filled completely before starting P . This doesn't happen in case 3 ,hence it is the answer.