Question

What is the lightest element on earth?

Answer 1

Hint : There are $118$ known elements present in nature till now. Each of these elements have different properties from one another. All these elements are arranged in a periodic table based on their properties to make their study easy to evaluate.

Complete Step By Step Answer:
Properties of the elements define them. Today in the periodic table we have s-block elements, d-block elements, p-block elements and the f-block elements.
The atomic weight of the elements is a characteristic of its structural composition i.e... Presence of electrons, protons and neutrons in it.
Among all the known elements on earth to date, we know that the simplest element is Hydrogen.
It has an atomic symbol as (H). Its atomic weight is $1$ .
Let’s look at its structural composition for better understanding:
Hydrogen has the atomic number as $1$ , it has one proton in its nucleus and $1$ electrons revolving around the nucleus in the atomic orbitals.
Important point to note is that the Hydrogen atom is the only element in the periodic table that does not have neutrons in its nucleus. So this makes the hydrogen atom the lightest of all elements.
Thus, on the basis of our above discussion we can easily say that the correct answer to our question is Hydrogen (H).
Therefore Hydrogen (H) is the lightest element on earth.

Note :
Hydrogen elements has two isotopes also i.e. Deuterium and tritium. These isotopes of hydrogen differ in the presence of neutrons in their nucleus. Deuterium possesses one electron, one proton and one neutron whereas tritium has one electron, one proton and two neutrons.