Learn Farsi: چرا شما بیرون اتاق ایستادید؟

It comes from the infinitive ایستادن (to stand). First, we find the past stem by dropping the -ن at the end, giving us ایستاد (stood). Because the subject is شما (you), we add the matching ending -ید to make ایستادید.

Can شما mean a single person here, or only a group?

It could be either! In Farsi, شما is used for a group of people (you all) or as a polite way to address one person. In both cases, the verb takes the exact same plural ending, -ید, just like we see in ایستادید.

How are the words بیرون (outside) and اتاق (room) linked when speaking?

They are linked by a hidden "e" sound called the ezāfe. When we say "outside the room," we pronounce it as birun-e otāgh. This short "e" connects the position word to the noun that follows it, even though it usually isn't written.

Why does the verb ایستادید come at the very end of the question?

In Farsi, the main verb almost always goes at the end of the sentence, even in questions. The order here is the question word (چرا), the subject (شما), the place (بیرون اتاق), and finally the verb (ایستادید).