Question

Approximately how many elements are in the universe?

Answer 1

The periodic table is an arrangement of all the known elements which are present in the universe, in an orderly manner according to their atomic numbers.
The elements present in the periodic table show periodic properties corresponding to their atomic numbers.

Complete step-by-step answer: If we consider the present scenario, there are $118$ elements which are known to us and are shown in the periodic table. The answer of this question may change with the discovery of new elements and so we cannot say for a fact that there are actually only $118$ elements in the whole universe.
These elements are classified on the basis of their atomic number and in the periodic table the elements show periodicity in properties, hence the name. The horizontal placement of the elements are called the periods, and the vertical placement of the elements are called groups.

Additional information: Now, we shall discuss some of these properties or the trends in the periodic table. If we consider the size of the elements, while going from left to right across a period the size of an atom decreases because with each consecutive period one electron is added to the outermost shell and the nuclear charge increases. However, from going top to bottom in a group, the size of the element increases as one outermost shell is added with each consecutive group progression.
If we consider the ionisation enthalpy of the elements which is the energy required to remove the most loosely bound electron from the outermost orbital of the isolated gaseous atom. The ionisation energy of an element decreases as we go down the group because the effective nuclear charge experienced by the outermost electrons decreases. And as we move from left to right the ionisation energy increases.

Note: There are about $118$ elements which are present in the universe which are known to us till date. However this number could change with the discovery of any new element.