mrlollersnakes

[oblique kestrel]

Please be patient

Our volunteers look into many questions every day; sometimes it takes them a little while to answer.

Pro tip: you can rename the thread title with `.tr <thread name>`

Make it descriptive, including relevant context, but also to the point. This way you improve your chances of getting a more relevant and specific answer.

[sharp sundial]

« besoin » is not formal

if you want to use that structure, 'which of X', you have to use « lequel »

« Lequel de ces livres voudriez-vous ? »
« Lequel d'entre eux voudriez-vous ? »
(I'm using « livre » because I'm assuming they're books)

Your example doesn't work because of two things:
(1) « quel (which) » requires a noun afterwards as it is an adjective. The « le » in « lequel (which one) » acts as a built-in placeholder. « Lequel de ces livres » can be thought of as « Quel livre de ces livres » if that suits your fancy. Do note that it has to agree in gender. Plural agreements depend on whether you want one of that noun or many of that noun.
« Lequel de ces fauteuils est-ce que vous voulez ? »
« Laquelle de ces tables est-ce que vous voulez ? »

(2) « de les » doesn't work because « les » can't function here. « les » is either an article or a direct object pronoun, none of which works (if it's an article, where's the noun and if it's a direct object pronoun, it doesn't have a verb that modifies it). You'd have to use the stressed pronoun. If you're using this, you'd have to use « d'entre [pronom] » instead of just « de [pronom] » because you're choosing one among a set.