why unser and not unsere?
(das) Zimmer is a neuter noun, the form of the neuter possessive pronoun in nominative is unser.
See https://en.wiktionary.org/wiki/unser#Inflection .
Its hard to enter special German characters from a mobile phone. Wish dou lingo had a tap screen for special characters for a phone
Shouldn't just "zimmer" or "raum" be accepted too?
No.
Zimmer and Raum are nouns and have to be capitalised.
They mean "room" but not "bedroom".