.The lightest or least dense metal that is a pure element is lithium, which has a density of 0.534 g/cm3. This makes lithium nearly half as dense as water, so if lithium was not so reactive, a chunk of the metal would float on water
The Correct Answer and Explanation is:
Lithium is the lightest metal that exists in its pure elemental form, with a density of 0.534 g/cm³. This density is significantly lower than that of water, which has a density of approximately 1.0 g/cm³. As a result, lithium is nearly half as dense as water. If lithium were not so chemically reactive, a chunk of it would indeed float on water.
The reason that most metals do not float on water is that they have densities greater than that of water. When an object is placed in a liquid, whether it sinks or floats depends on its density relative to the liquid. Objects with a density less than the liquid will float, while objects with a density greater than the liquid will sink. Water’s density is the threshold for this comparison. Since lithium’s density is so low, it would float in water if it were not for its chemical reactivity.
Lithium is highly reactive, especially with water. When it comes into contact with water, it reacts vigorously, producing heat and hydrogen gas. This reaction is exothermic, meaning it releases energy. The heat produced during this reaction is sufficient to ignite the hydrogen gas that is released, making lithium one of the most reactive metals in the periodic table. This reactivity prevents chunks of lithium from floating on water without undergoing a violent reaction, unlike less reactive metals such as sodium or potassium, which can also float on water but still react to a lesser extent.
So, despite lithium’s low density, which would allow it to float, its extreme reactivity with water overrides this physical property.
