" 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
