What is the highest occupied molecular orbital in the o2 molecule?

HOMO

Oxygen molecule i.e. O₂ has total 16 electrons.

Electron configuration of O₂ is 1s² 2s² 2p⁴

On placing the electrons in molecular orbitals according to Aufbau's Principle and Hund's Principle. So, there are two electrons in the orbital that is the highest occupied molecular orbital.

Hence O₂ is paramagnetic in nature since it has two unpaired electrons.

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H2 is known to exist. For dihydrogen, H2, we can identify the frontier molecular orbitals (FMOs). The highest occupied molecular orbital (or HOMO) is the σ (sigma) 1s MO. The lowest unoccupied MO (LUMO) is the σ* (sigma star) 1s MO which is antibonding.

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm