Which number is rational, square root 2, pi, square root 10 or square 16

The square root of 16 is rational.

Answer: The only rational number in your list is "square 16" - I am assuming you mean square root of 16.

Explanation:

Square root of 2 is irrational. This has been proven by the Pythagoreans (there is a simple proof of that).

pi is also known to be irrational although the proof is a bit more demanding.

Square root of 10 can be written as a product of square root of 5 and square root of 2, which themselves are irrational. Any product involving an irrational number is irrational

Square root of 16 = 4. 4 can be written as a fraction 4/1, or 8/2, 16/4, etc. and therefore is rational by definition.