"Our bedroom is big."

Translation: Unser Schlafzimmer ist groß.

[Javier65949]

why unser and not unsere?

[quis_lib_duo]

(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 .

[RobS961646]

Its hard to enter special German characters from a mobile phone. Wish dou lingo had a tap screen for special characters for a phone

[na-prablenia]

Shouldn't just "zimmer" or "raum" be accepted too?

[mizinamo]

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".