Final answer:
Irrational numbers cannot be expressed as a fraction or the ratio of two integers. The numbers 21.10675..., 0.011, and -9.72827... are irrational numbers.
Step-by-step explanation:
An irrational number is a number that cannot be expressed as a fraction or the ratio of two integers. It is a number that cannot be written as a terminating or repeating decimal. In the given options, the numbers 21.10675..., 0.011, and -9.72827... are irrational numbers.
Example: The number 21.10675... is irrational because it cannot be expressed as a fraction. It goes on forever without repeating and doesn't terminate.