You considered the situation of moving a couch at a constant speed. You concluded that to move the couch at a constant speed, you would need to push it with a force that exactly balances the frictional force of 50 N acting on the couch. Now consider a situation in which the couch is at rest. You push on the couch with a force of 25 N--and the couch still does not move. Which one of the force diagrams below best describes this situation?

The couch will remain stationary

Explanation:

Friction is the force that resist/opposes the  motion. It is the force that has to e overcome before an object can move.

Since the frictional force of 50 N  is required before the couch can move, applying 25 N can not overcome the frictional force of 50 N, so the couch will remain stationary.A force greater than 50 will be require to set the couch in motion

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