How many unpaired electrons are present in each of the following ground state atoms :
a) O and b) As 

Explanation

a) `O (Z = 8) = [He] 2s^(2)2p_(x)^(2)2p_(y)^(2)2p_(y)^(1)2p_(z)^(1)`. Number of unpaired electrons = 2
b) As `(Z = 33) = [Ar] `4s^(2)3d^(10)4p_(x)^(1)4p_(y)^(1)4p_(z)^(1)`. Number of unpaired electrons = 3