Irrational numbers are numbers that can not be expressed in a fraction of two whole numbers.
The given number "0.212121" is a repeating decimal number, because the decimal follows a particular repeated pattern. Since the number is a repeating decimal number, it is also an irrational number because repeating decimal numbers can not be expressed in a fraction of two whole numbers.
Therefore, "0.212121" is an Irrational Number.
