Lithium be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than
Dense set space "X" is the least cardinality of a dense subset of "X". An alternative definition of dense set in the case of metric spaces is the following. When the topology of "X" is given by a metric, the closure formula_1 of "A" in "X" is the union of "A" and the set of all limits of sequences of elements in "A" (its "limit points"), Then "A" is dense in "X" if Note that formula_4. If formula_5 is a sequence of dense open sets in a complete metric space, "X", then formula_6 is also dense in "X". This fact is one