Questions & Answers about Det är farligt för en att röka.
Why do we use en here instead of man?
man is the subject form of the generic pronoun. In this sentence, the pronoun comes right after the preposition för (for), which means it must be in the object form. The object form of man is en.
The translation says "you", but doesn't en mean "a" or "one"?
It can be the number one or the word "a/an"! But here, en is acting as the object form of man. While the literal translation is "It is dangerous for one to smoke", native English speakers usually use a generic "you" for this kind of statement. It refers to people in general, not you personally.
Why does the adjective farligt end in a -t?
It is agreeing with the pronoun Det (It). When you start a sentence with Det är... (It is...) to describe a general situation or an action, the adjective must be in its neuter form, which usually means adding a -t.
Do I need att in this sentence?
Yes, att is the infinitive marker, functioning exactly like the word "to" in the English phrase "to smoke". You need it to connect the base verb röka (smoke) to the rest of the thought.