Question

The lightest metal among the following is
(1) Cs
(2) Be
(3) Na
(4) Li

Answer 1

Hint: This lightest metal is a soft, silvery-white alkali metal with atomic number of 3. Under standard conditions, it is the lightest metal and the lightest solid element too. For related reasons, this element has important uses in nuclear physics.

Complete step by step answer:
The pure element which is the lightest or least dense metal is lithium. It has a density of \[0.534\dfrac{g}{{c{m^3}}}\]. This makes lithium nearly half as dense as water that’s why if lithium was not so reactive, a chunk of the metal would float on water. The secret of lithium's success is that it is the third element of the periodic table, after the gas’s hydrogen and helium. Its simple atoms contain just three protons each and make lithium the lightest of all metals. Because of being so light, the atoms slip easily between the layered materials that make up the battery. Thus, Li is the lightest metal because it is placed in the first group of periodic tables i.e. in the alkali metal group and it has the lowest atomic number.

Therefore, the correct answer is option (4).

Note: Lithium floats in the lightest of mineral oils, and would handily do so on water as well if not for another of its unusual properties, an extremely high reactivity. Lithium reacts with water, tarnishes on contact with atmospheric oxygen and will even burn in nitrogen. It is happy to give its outermost valence electron to anyone who will take it, disrupting even the highly stable triple bond in molecular nitrogen. Lithium is also capable of intercalation into the crystal structure of other materials, notably graphite and metal oxides.