Answer
2
Step-by-step explanation
According to the Aufbau Principle, electrons fill the subshells in order of their increasing energy level.
For an oxygen atom having atomic number 8, the electron configuration will be:
1s² 2s² 2p⁴
The P subshell has three orbitals which are degenerate orbitals. According to Hund's rule of maximum multiplicity, two or more orbitals of equal energy electrons will occupy them singly before filling them in pairs.
Thus for oxygen, the p orbitals will be filled like:
2px² 2py¹ 2pz¹
Therefore, an oxygen atom in its ground state has two unpaired electrons.