Tollen's reagent and Fehling solution distinguish many elements in the same functional classes, how do they distinguish carbonyl compounds ( aldehydes and ketones ).
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Ibelieve the answer is d

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.

Idon't know hope someone you