An atom or a group of atoms with at least one unpaired electron.
2
这种反应，需要催化剂，将甲醇和水变成质子和电子（换句话说，就是游离的氢原子）以及二氧化碳。
The reaction, which requires a catalyst, turns the methanol and water into protons and electrons (in other words, dissociated hydrogen atoms) and carbon dioxide.
3
光击中这种蛋白质产生一对游离的活性基，这是一种非常活跃的有着不成对的电子的分子。
Light hitting the proteins produces a pair of free radicals, highly reactive molecules with unpaired electrons.
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