Ownership can be defined as the state or rights owned by someone over something. It could be land, property, house, etc. When you own something it becomes your possession.
And ownership of a space means the rights of possessing or owning of a particular area.
The examples mentioned in the options all belongs to ownership of a space.
In first option, the person possesses the rights of his own home by locking it, which means if someone who does not belong to that house needs permission of the owner of the house.
In the second one, the nameplate on the door of an office reveals that the office belongs to a particular person and run by him, and that particular person is responsible for running of that office.
Third option reveals the ownership of a seat, which is assigned to him. And he needs to sit on the particular seat assigned to him.
