Sentence:  Serial serum <WSD>potassium</WSD> levels remained normal ; the serum glutamic oxaloacetic transaminase was 10 units per ml. per min. . 
Meaning of the word marked with <WSD> tags:  a light soft silver-white metallic element of the alkali metal group; oxidizes rapidly in air and reacts violently with water; is abundant in nature in combined forms occurring in sea water and in carnallite and kainite and sylvite