Object Orientation in VB.NET

I have got a program where I should extensively implement
object-oriented features of the vb.net. I have got a class tenant and a
class room, both belong to some dormitory. In that dormitory class i
have 2 array lists to store objects of class tenant and room
respectively. In class tenant I created association with the class
room, so I may see in which room every tenant lives. However I did not
create association in the room class in order to avoid data
duplication.

Instead if I want to lookup which tenant lives in some particular room,
I first get the room number from the rooms array list and then I lookup
the same room no in the tents list and retrieve the corresponding
tenant's name.

I am not sure whether this approach is fine, anyway it provides me info
I need. But I am not sure whether it is object oriented enough? Should
I create an association to tenant class in the room class?

Someone told me that class should be a complete entity and hold all the
info it is supposed to hold. I would like to get your opinion in that.

.