The incorrectly spelt word in the options is "Plecard." The correct spelling is "Placard."

Here is the detailed explanation for each option:

• Slippers: This is the correct spelling, referring to a type of comfortable footwear typically worn indoors.
• Plecard: This is the incorrectly spelt word. The correct spelling is "Placard," which refers to a sign or notice displayed in a public place.
• Banner: This is the correct spelling, referring to a long strip of cloth or material with a message or design displayed in public.
• Monument: This is the correct spelling, referring to a structure or statue built to commemorate a person, event, or significant historical or cultural significance.