Sentence:  A wall stabilized high current arc source was constructed and used to study transition probabilities of atomic hydrogen and <WSD>oxygen</WSD> . 
Meaning of the word marked with <WSD> tags:  a nonmetallic bivalent element that is normally a colorless odorless tasteless nonflammable diatomic gas; constitutes 21 percent of the atmosphere by volume; the most abundant element in the earth's crust