Let, a = 0.2101
And, b = 0.2222...
We observe that in the second decimal place a has digit 1 and b has digit 2, therefore a < b . in the third decimal place a has digit 0. So, if we consider irrational numbers
x = 0.211011001100011....
We find that
a < x < b
Hence, x is required an irrational number.