Which phrase is more correct, "one" or "the one"?

There are two oranges on the table. Which one do you want?

I want the one on the right.

I need a banana.

I'll get you one from the bunch in the kitchen.

Bring me the one that looks the ripest.

b is correct if the supermarket has only one orange. In other words, a is correct.

You can use either, but they change the meaning.

a is more usual and means you will go and buy an orange

b suggests there is only one orange left in the supermarket

and you will be going to buy that very one.

So only use 'the one' if talking about a specific item.

Bonus - 'correct' is an absolute: so something cannot be more or less correct than another.

a correct

b for dramatic effect but not for buying oranges

the one is used for dramatic effect

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