"Quelles chaussures ?" is indeed a plural form. The singular form is "quelle chaussure ?".
In oral French, there is absolutely no difference between the plural and the singular forms.
Maybe if there were a bit of context, you would know which...
Example : "quelles chaussures pour aller à l'Opéra ?" or "quelle chaussure as-tu mise en premier ?" (which shoes to go to the Opera? - which shoe did you put on first?)
Quel, quelle, quels, quelles: interrogative or relative adjectives which modify nouns.
- quel jour sommes-nous ? (what day is it today?)
- je me demande quel jour il viendra (I am wondering which day he will come)
Lequel, laquelle, lesquels, lesquelles: interrogative or relative pronouns.
- lequel est ton chapeau ? (which one is your hat?)
- parmi tous ces chapeaux, je me demande lequel il va choisir (among all these hats, I am wondering which (one) he will choose)
Auquel, à laquelle, auxquels, auxquelles: interrogative or relative pronouns used with constructions requiring preposition "à".
- Il y avait plusieurs personnes; à laquelle parlais-tu ? (there were several people; to which were you talking to?)
- j'aimerais savoir à laquelle de ces personnes tu parlais (I would like to know to which of these people you were talking)
Duquel, de laquelle, desquels, desquelles: interrogative or relative pronouns used with constructions requiring preposition "de".
- Entre ces deux hommes, duquel pourrais-tu tomber amoureuse ? (of these two men, with whom could you fall in love?)
- Les filles desquelles j'avais entendu parler (the girls of whom I had heard)
Note: "dont" (relative pronoun) or "de qui" (interrogative) easily and often replace "duquel, de laquelle, etc": - Entre ces deux hommes, de qui pourrais-tu tomber amoureuse ? - Les filles dont j'avais entendu parler.
This lesson is an enormous leap for me from the last and I am struggling with it for the embarrassing reason that I simply have lost so much grammar of my own native tongue (English) Also my age is of no assistance at all to my memory. Obviously I shall be here, on this lesson revising ad nauseum. This is no bad thing. I have, to date, made reams of notes which I study when offline and they help instill into my thick skull some of that which I have recently learned. The threads are very helpful and of the thousands which I have studied only two were somewhat uncomfortable to experience. This shows the inclusiveness and loveliness of the students here. It is OK to be apparently ignorant, dumb even... its not against the law nor Duo's rules, nor beyond the tolerance of the helpers. Heck, even I have helped and I seem to be from Mars! :)