Q No. of unpaired electrons in O₂ molecule---

1) 0      2)1        3) 2            4) 4

see O2 does not hav a unpaired electron but

well if u draw the molecular orbital diagram of O2

then u will get a unpaired electron configuration

hence it is paramagnetic.

if you write the MO configuration for oxygen molecule it is   seen that there are two unpaired electrons in antibondin p-orbital

O₂ molecule possesses 4 unpaired electrons...