Learn Spanish (Spain): ¿A vosotros os interesa el arte moderno?

Verbs like interesar work exactly like the verb gustar. The sentence literally translates to "Does modern art interest to you guys?" Because the real subject of the sentence is el arte moderno (a single thing), the verb is in the "it" form: interesa.

Why do we need both a vosotros and os in this sentence?

In this sentence, os is the mandatory pronoun that means "to you guys". The phrase a vosotros is optional and adds emphasis. It is like asking, "Are you guys (as opposed to someone else) interested in modern art?"

Why is there an el before arte moderno? We don't say "the modern art" in English.

In Spanish, when you talk about general concepts, likes, or dislikes as the subject of a sentence, you must include the definite article (el, la, los, or las). Since modern art is the subject here, it needs el.

Is arte masculine?

Yes, in its singular form, arte is masculine. That is why it uses el and why the descriptive word moderno ends in -o to match it.