The rational numbers are those which can be written in the form p/q where 'q' is non zero.
The irrational numbers are those which cannot be written in the form p/q where 'q' is non zero.
Since the two are exactly opposite in nature, they cannot have any element in common, i.e. there cannot exist a number which is rational as well as an irrational number.
So the set of rational numbers and set of irrational numbers must be disjoint.
Therefore, both sets will be represented as separate circles in the Venn diagram representation.
So the option A is the correct choice.