If You Were Presented With Three Items,

[sandyRoe]

an apple, a potato, and an onion, and asked which is the odd one out, what would you say?

I'd go for potato because it originated in the Americas.

I believe this was part of the entrance exam to an Oxbridge university, and there's no right answer.

[ferlew]

I'd say apple, because the other two are grown under the earth.
You werelistening to Radio Four then, same as me this afternoon.

[Bazile]

Apple cos it's grown in the soil , like the other two 

[Atheist]

There isn't a right answer. And onions aren't grown underground; when the onion plant grows and matures, the bulb usually sits mostly above ground.

[barry1010]

AI says apple because it is a fruit.

I'd say potato because I can eat an apple and an onion raw

[Atheist]

You could say, onion doesn't have a letter 'a' in it.

[Bazile]

cos it's not grown 

[theshedman]

I would have said apple as it's a fruit the other 2 vegetables.

[DTCwordfan]

apple, the other two are root veg.

The story I like is a prospective student being interviewed  at Oxford, Oriel I believe.... November, late afternoon and he walked into the Prof's study and was invited to sit down, the Prof sitting there with one desk-lamp on and reading The Times - the newspaper being held up.

A couple of minutes pass and then the Prof lowers the newspaper and, over his horn-rimmed half-moon reading glasses, looked at the prospective student and said, "Prove that you are brilliant!"

The student reached inside his pockets, pulls out a lighter and sets fire to the newspaper.....

 

[barry1010]

Onions and potatoes are attached to the roots, apples are attached to branches

[Bazile]

Apple cos you can't make Apple crumble with the others 

[Barmaid]

Apple because onion and spuds would taste awful with custard.

[Squitty]

potato because if you cut them through the centre the potato is flesh all the way but apples and onions have a definate centre

[THECORBYLOON]

It could be onion because in French, "pomme" is an apple and "pomme de terre" is a tattie.

[netherfield]

Could be the Onion, it's the only one that grows in layers. And you can't pickle an Apple or a Potato.

[Hopkirk]

Onion, because I like apples and potatoes 

[Canary42]

Potato because you can make a tart with the other two.

[Arksided]

Apple the others have two set's of the same letter

[Togo]

And you can't pickle an Apple or a Potato.

Apple Chutney and salt n vinegar crisps. Yum.🥖🧀🍺

[ToraToraTora]

apple because it's fruit.