Police stop a truck at a check post which claims to be carrying sacks of Humic Acid Sodium, a black, water-soluble fertilizer. When the truck is examined, it is found to have sacks of at least four different materials which the police label W, X, Y and Z. They suspect that apart from the fertilizer, the truck is carrying iron filings, gunpowder, and black powdered wood. They conduct some tests whose results are as follows: The real question is to look at the table and find out which one is the gunpowder?