Learn Hardcore Catalan: Quan arribin les convidades, la meva mare servirà l'amanida i jo serviré el pa. - When the guests arrive, my mother will serve the salad and I will serve the bread.

Breakdown of Quan arribin les convidades, la meva mare servirà l'amanida i jo serviré el pa.

Why is it Quan arribin and not Quan arriben?

Because this quan-clause refers to a future event that has not happened yet. In Catalan, that usually calls for the present subjunctive:

If you say quan arriben, it more often sounds like a habitual or repeated situation:

Quan arriben les convidades, sempre obrim una ampolla de vi.
= When the guests arrive / Whenever the guests arrive, we always open a bottle of wine.

So in your sentence, arribin is the normal form.

What exactly is arribin?

Arribin is the present subjunctive, 3rd person plural, of arribar.

Here is the pattern:

In the sentence, it matches les convidades, which is a plural subject, so arribin is the correct form.

Could I say Quan arribaran les convidades here?