Explain why the quantum number set (2, 1, -2, -1/2) is not possible for an electron in an atom.

" n " is called principle quantum number. Here , n = 2 which means , number of shells = 2 .: l ( azimuthal quantum no: ) / ( n - 1 ) = 0 , 1 & m ( magnetic quantum number ) = -1 , 0 , +1 s ( spin quantum number ) = ± 1/2 Coming to this question , here n = 2 l = 1 ( possible ) ml = -2 [ not possible , because it can only be a number from this set ( -1 , 0 , +1 ) ] .: this set is not possible

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