Complex sentence: At room temperature, O 2 exists in a triplet state, which would require the forbidden transition into a singlet state before a chemical reaction could commence, which makes it kinetically nonreactive despite being thermodynamically a strong oxidant.
Split into simpler sentences: At room temperature, O 2 exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive despite being thermodynamically a strong oxidant.