Which phrase from the paragraph best helps the reader understand the meaning of the underlined word? Kate wanted to remove some tarnish from some old silverware. First, she put the silverware in a pan on top of aluminum foil. Then she sprinkled baking soda and salt over the utensils. As soon as Kate poured boiling water over the silver, the water bubbled up quickly. It acted as a catalyst. In no time, most of the tarnish was removed.