"The water is not red."
Translation:La akvo ne estas ruĝa.
Although word order is much less significant in Esperanto than English, you still need to place negation before the verb you're negating.
So it has to be ne estas in this case. If you just want to say that The water is non-red, you can get creative and use malruĝa!
i did it the way memyself asked and I got it right. Is the answer key wrong or did you make a mistake?
I'm guilty of contracting this way. I also often just say "Sa!" rather than "Saluton!" just out of laziness. XD
I've also said: Mi'stas=Mi estas Ci'stas=Ci estas, and so on and so forth....
Can it also be 'la akvo rugxa ne estas' I really like the format of having verbs at the ending of sentences (mostly because It helps me with learning other languages that have this format) or is there a more regulated rule about this?
Even if theorically the order is totally free, you must avoid possible misunderstandings. In your example most of people would understand "The red water is not (here/present)."
I'd imagine it might sound that way in speech, or you could do it to get one less syllable in poetry, but it's nonstandard and I might be wrong even about the poetry use.
I worte rugXan instead of rugXa, and I was wrong. What is the correct time to use -n?
It's not unusual actually, it's just an intransitive verb, so, like all intransitive verbs (to go, to fall, etc...), it can't have an object, so there's no use for "-n"
It is wrong. -n is used for the object of a transitive predicate, so you don't use it with "be".
Because you aren't supposed to use the accusative ending "-n" on words that come after the verb "estas."
Ŝi havas rozon floron. - She has a pink flower. (Note how the "-n" ending is used.) Ĝi ne estas rozo floro. - It is not a pink flower. (Note how the "-n" ending is NOT used.)
I hope this helps! :)