Question

The lightest metal is:
(A) Li
(B) Fe
(C) Cu
(D) Ag

Answer 1

The metal which has lowest density will be called the lightest. Density of a metal is the ratio of the mass of the metal to its volume. The lightest metal is used to treat bipolar disorders.

Complete step by step answer:
- We will need to compare the density of the given metals in order to find out which one will be the lightest.
- Density is the ratio of mass of the atom to its volume.
- Density increases as we go down the group in the periodic table as the atoms get heavier.
- As we compare the density of the group-1 and group-2 elements, group-2 elements have smaller volume of the atom because of the decreased atomic radius and there is an increase in the number of protons as the atomic number increases. So, group-2 elements are denser.
- So we can say that group-1 elements will be the lightest amongst the elements of other groups. This happens because as we go from left to right in the periodic table, positive charge in the nucleus increases and that decreases the atomic radius and that results in an increase in the density of the atom.
- Fe, Cu and Ag are the elements of the d-block. So, they are arranged in the right hand side form the group-1 elements. Li is an alkali metal and therefore it is a group-1 element.
- So, we can say that Li is the lightest metal.

So, correct answer is (A) Li

Note: Note that Li is the lightest metal amongst the alkali metals as well. However the density of Sodium is more than that of Potassium even though potassium is in its third period. The order of density of the alkali metals is as below.
Li < K < Na < Rb < Cs