Which sentence is nonstandard in its preposition placement?
The laptop that I logged in on is in the lab.
The laptop on which I logged in is in the lab.
The laptop which I logged in on is in the lab.
The laptop on that I logged in is in the lab.✓Richtige Antwort
Erklärung
On cannot be fronted before that, so that sentence violates the form required by preposition fronting. The other sentences use either legitimate stranding or the formal combination of on with which.