What does 了mean in 衣服也落在了房间内, and is it pronounce le or liao?
衣服也落在房间内*了*。

Here 了 is used to indicate the completion of the action of 落在房间内.

衣服也落在*了*房间内。

Here 了 is moved forward and positioned after 在, and that makes 房间内 become the focus point of this setence.

Other examples: 
一阵大风吹来，我的帽子飞到*了*天上。

他开车撞到*了*树上。

他把狗锁在*了*屋内。

她一挥手碰翻*了*水杯。