Which number has an irrational square root?

The number with an irrational square root from the options given is 2.

Here’s a short explanation:

– The square roots of 9 (3), 4 (2), 1 (1), and 81 (9) are all whole numbers, making them rational.

– However, the square root of 2 is approximately 1.414, which cannot be expressed as a fraction of two integers, therefore it is irrational.

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