Directions: Select the most appropriate one-word substitution for the given words.
A large bedroom for a number of people in a school or institution

Let's check the definitions of the words:
Dormitory: A large bedroom for a number of people in a school or institution.

Mansion: A large, impressive house.

Cloakroom: A room in a public building where outdoor coats and luggage may be left.

Observatory: A room or building housing a telescope or other scientific equipment for the study of natural phenomena.