Final answer:
C) Lithium. Lithium (Li) is the only alkali metal that melts at a temperature higher than the boiling point of water, with a melting point of about 180°C.
Step-by-step explanation:
The only alkali metal that melts above the boiling point of water is Lithium (Li). Each alkali metal has a different melting point. As an example, sodium (Na) and potassium (K) both have melting points that are lower than the boiling point of water, which is 100°C. However, lithium, with a melting point of about 180°C, melts at a temperature higher than the boiling point of water. Cesium (Cs), on the other hand, has one of the lowest melting points among the alkali metals and melts at about 28°C.
Although all alkali metals are highly reactive and have similar chemical properties, their physical properties such as melting points vary. Knowing the unique characteristics of each alkali metal helps in understanding their applications and potential hazards when handling them. For instance, lithium is widely used in batteries and certain medical treatments, precisely because of its distinct properties compared to other alkali metals.