Learn Portuguese (Portugal): O quarto tem um terraço luminoso, atrás do qual está o jardim. - The bedroom has a bright terrace, behind which is the garden.

After multi-syllable prepositions like atrás, Portuguese requires us to use the relative pronoun o qual (or a qual, etc.) instead of the simpler que. Because 'behind' is atrás de, the preposition de combines with o qual to form do qual.

How do I know whether to use do qual, da qual, dos quais, or das quais in this sentence?

The relative pronoun has to match the gender and number of the noun it refers back to. Here, 'which' refers to the terrace (um terraço), which is masculine singular, so we use o qual (combined with de to make do qual). If it were a balcony (uma varanda), we would use da qual.

Why is the verb estar (está) used for the garden? Isn't a garden permanent?

Yes, but European Portuguese uses estar to describe the physical location of objects, buildings, and places, regardless of whether they are permanent or temporary. Therefore, we use está to state where the garden is situated.

Is it wrong to say atrás do qual o jardim está?