Which of the following species contain unpaired electron?

(a) KO2 (b) AlO2(-1ve) (c) NO2(+1 ve) (d) BaO2

please tell how?

If you make the structures of the following componds then these will exists like above:

And It seems me that KO2 has unpaired elctrons.

Answer will be BaO2
here oxidation number of Ba is +1
Ba(+) has 1 electron in its outermost shell so its unpaired

in KO2 . .oxd state of K is +1 so no unpaired electrons(noble gas config for K)

in AlO2(-) . . oxd state of Al is +3 so no unpaired electrons

in NO2(+). . oxd no of N is +5 so no unpaired electrons(noble gas config for N) 

Please approve 

Ba(+) has 1 electron in its outermost shell so its unpaired

in KO2 . .oxd state of K is +1 so no unpaired electrons(noble gas config for K)

in AlO2(-) . . oxd state of Al is +3 so no unpaired electrons

in NO2(+). . oxd no of N is +5 so no unpaired electrons(noble gas config for N) 

Please approve 

Ko2