The correct set of four quantum number for the unpaired electron of the element Z = 21 is

Options

A. `n=3 , l =2 m =1 s=+1/2`
B. `n=3 , l =1 m =0 s=+1/2`
C. `n=3 , l =3 m =2 s=+1/2`
D. `n=4 , l =0 m =0 s=+1/2`

Answer

A

Explanation

The element Z = 21 is Sc. Electron configuration of it is : `Is^(2) 2s^(2)2p^(6) 3s^(2)3p^(6) 4s^(2) 3d^(3)` The unpaired electron of Z - 21 is `3d^(3)`
(i) n = 3 = principal quantum number
(ii) d orbital has l=2
(iii) as l=2 values of m =+2,1 ,0,-1 ,-2 `therefore` m=+1 is possible but only (A) has l=2
(iv) first electron in 3d has spin quantum no =+`1/2`
thus n=3, l=2,m=1 and s=`+1/3`