Learn Hardcore Swedish: Han blir ofta stressad av mörka rum.

Blir is the present tense of bli (to become). Here it means “becomes/gets,” so the sentence means “He often gets stressed by dark rooms.” With ofta (often), it describes a habitual tendency.

Why is ofta placed after blir? Where do adverbs go in Swedish main clauses?

Swedish follows the V2 (verb-second) rule: the finite verb must be in second position. In a neutral main clause with a subject first, the verb comes next, and then come mid-field adverbs like ofta:

Han [blir] ofta [stressad av mörka rum]. If you front something else (like an adverb), you invert:
Ofta blir han stressad av mörka rum.

Can I say Han blir stressad ofta av mörka rum?

It’s not idiomatic. Swedish strongly prefers Han blir ofta stressad av mörka rum or, with fronting, Ofta blir han stressad av mörka rum. Placing ofta at the end or after the adjective sounds odd in this sentence.

What’s the difference between blir and är here?

blir = becomes/gets (a change of state triggered by something): Han blir ofta stressad av mörka rum.
är = is (a state): Han är ofta stressad i mörka rum. Both can be natural; blir emphasizes the trigger/change, är the ongoing state in that situation.

Why is it stressad and not stressigt or stressande?

stressad describes a person who feels stressed: Jag blir stressad (I get stressed).
stressig(t) describes something hectic/stressful: En stressig dag; Det är stressigt på jobbet.
stressande describes something that causes stress (often as a general property or activity): Det är stressande att köa i timmar. In your sentence, we describe his feeling, so stressad is right.

Why stressad and not stressat?

Predicative adjectives agree with the subject’s gender/number:

Han är stressad. (common gender singular)
Barnet är stressat. (neuter singular)
De är stressade. (plural) Since han is common gender, it’s stressad.

What does av mean here, and are there alternatives?

Av here means “by/from” in the sense of cause: stressad av mörka rum = “stressed by dark rooms.” Alternatives:

över (“about/over”) for worries about something abstract: stressad över tentan (the exam).
i for location: stressad i mörka rum (stressed in dark rooms).
på grund av (“because of”) is more explicit/formal: stressad på grund av mörka rum.
av att
- infinitive clause for an action: stressad av att vara i mörka rum.
Before upcoming events, inför is common: stressad inför intervjun. Avoid stressad för in this meaning.

Why is it mörka rum and not mörkt rum or mörk rum?

Because we’re talking about plural “rooms.” Rum is an ett-word whose indefinite plural is also rum (no ending), and adjectives take -a in the indefinite plural:

mörka rum = dark rooms (indefinite plural) For reference:
ett mörkt rum = a dark room (singular, neuter → adjective gets -t)
mörka rum = dark rooms (plural → adjective gets -a)
det mörka rummet = the dark room
de mörka rummen = the dark rooms So mörk rum is ungrammatical; it must be mörkt (singular neuter) or mörka (plural/definite).

Could I say av mörker or av ett mörkt rum instead?

Yes, with different nuance:

av mörker = by darkness (general).
av mörkret = by the darkness (definite, specific).
av ett mörkt rum = by a (particular) dark room. The original av mörka rum talks about dark rooms in general as a category.

How do I negate this, and where does inte go?

Place inte after the finite verb:

Han blir inte stressad av mörka rum. (He doesn’t get stressed by dark rooms.) If you mean “not often,” Swedish prefers sällan:
Han blir sällan stressad av mörka rum. Note the difference:
Han blir inte ofta stressad … = not often (somewhat formal/marked).
Han blir ofta inte stressad … = he often is not stressed (different meaning).

How would I put this in other tenses or express “usually”?

Past: Han blev ofta stressad av mörka rum.
Present perfect: Han har ofta blivit stressad av mörka rum. (Note ofta after har.)
Future: Han kommer (ofta) att bli stressad av mörka rum.
“Usually” with brukar: Han brukar bli stressad i mörka rum.

Can I front the location or the cause for emphasis?

Yes. Keep the verb second:

Location focus: I mörka rum blir han ofta stressad.
Cause focus: Av mörka rum blir han ofta stressad.

Any quick pronunciation tips for key words?

han: “hahn,” short a.
blir: “bleer,” long i.
ofta: “OF-ta,” both f and t pronounced.
stressad: “STRESS-ad,” short e, double-s feeling.
mörka: “MUR-ka,” with Swedish ö (like the vowel in English “fur,” but more rounded).
rum: Swedish u is a compressed, rounded sound between “ee” and “oo.” Swedish r is usually tapped or slightly trilled before consonants.