Which of the following is NOT a characteristic of mortise locks according to standard practice?

• A. They are recessed into the door
• B. They are used when a door knob or latch is required
• C. They are mounted on the surface of the door
• D. They are found in building entrance doors

Answer: (C)

Mortise locks are installed by cutting a pocket into the edge of the door so the lock body sits recessed inside the door, with a faceplate flush with the edge. That recessed, embedded installation is what defines a mortise lock.

Because of that setup, the statement about being mounted on the surface is not a characteristic of mortise locks. They’re designed to live inside the door, not on its surface.

The other statements fit standard practice: being recessed into the door is exactly how they’re installed; they’re used on doors that need a robust latch and often work with a door knob or lever to operate that latch; and they’re commonly found on building entrance doors where extra security and durability are desirable.