The term U, V, W or Y, but not X is an ELEMENT, which is a type of chemical substance that cannot be broken down into simpler substances by ordinary chemical processes. This ELEMENT is composed of atoms that are all the same, and it cannot be separated into different types of matter. The elements U, V, W and Y are all found in the periodic table, and they are all non-metals. U is uranium, V is vanadium, W is tungsten, and Y is yttrium.