Choose the odd one out: 250, 196, 225, 289.

196 is 14 squared, 225 is 15 squared and 289 is 17 squared, so each is a perfect square. 250 lies between 225 and 256 (16 squared) and is no square at all. It is tempting because it is a round number that looks orderly beside the others, but roundness is not the property being tested.