Question

Among the elements from atomic number $1$ to $36$, the number of elements which have an unpaired electron in their $s$ subshell is

• A. 7
• B. 9
• C. 4
• D. 6

Answer 1

Answer: (D)

6

Answer 2

Among the elements from atomic number to 36, following six elements have an unpaired electron in their s-subshell.

${ }_{1} H =1 s^{1}$
${ }_{3} Li =1 s^{2},\, 2 s^{1}$
${ }_{11} Na =1 s^{2},\, 2 s^{2}\, 2 p^{6},\, 3 s^{1}$
${ }_{19} K =1 s^{2},\, 2 s^{2}\, 2 p^{6},\, 3 s^{2}\, 3 p^{6},\, 4 s^{1}$
${ }_{24} Cr =1 s^{2},\, 2 s^{2}\, 2 p^{6},\, 3 s^{2}\, 3 p^{6},\, 4 s^{1},\, 3 d^{5}$
${ }_{29} Cu =1 s^{2},\, 2 s^{2}\, 2 p^{6},\, 3 s^{2}\, 3 p^{6},\, 4 s^{1},\, 3 d^{10}$