"Did something happen yesterday?"
Translation:Ist gestern was passiert?
Could you please explain the word order here? I would have gone "ist was gestern passiert"
That emphasises gestern more than normal, but should probably also be accepted.
The general rule is that the most-relevant information to the verb goes nearer to the end. The verb is "happened" and the natural first question to this is "what happened?", so the "what" information goes closest to the end. Other information like "when?", "to whom?", "how?", etc. is secondary.
There's a good series explaining it here: https://yourdailygerman.com/2015/01/07/german-word-order/
Why the word 'something' was not translated in the sentence? Etwas?
"Was" can also mean "etWAS", but I don't know why is "etwas" not acceptable here.
Ist gestern etwas passiert? should be accepted, as far as I can tell.
That's possible, though a bit formal.
Passierte gestern etwas? sounds a bit better to me for some reason.
Neither is on the list of accepted alternatives; you can report them if you'd like.
That's not possible. passieren uses sein to form the perfect tense, so it would be Ist gestern etwas passiert?
I would say that "passieren" is certainly a change of state; if something is happening, then there's definitely some sort of change happening. (If there's no change, nothing happened.)
If that doesn't help you, there are some verbs that you just have to know use "ist" (like "bleiben," which is quite distinctly not any sort of change).
The most common question would use gestern as a topic and place it first -- Ist gestern etwas passiert?, for example.
(The effect of topicalising gestern is a bit like "Yesterday -- did anything happen then?", though it sounds more natural in German.)
Ist etwas gestern passiert? would sound more like "Something -- did it happen yesterday? (As opposed to on some other day?)". Which might be a possible translation of the English, since stress isn't marked ("Did something happen YESTERDAY?"), but is a less likely translation.