Sentence:  These widely advertised products , which are used primarily for washing clothes , are based on high-sudsing , synthetic organic actives ( <WSD>sodium</WSD> alkylbenzenesulfonates ) and contain up to 50 % by weight of sodium tripolyphosphate or a mixture of sodium tripolyphosphate and tetrasodium pyrophosphate . 
Meaning of the word marked with <WSD> tags:  a silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite (rock salt)