Answer:
Have you seen Margot's mitten?
Explanation:
A possessive noun is a word construction that shows the possession or ownership of a thing by someone. This is done by adding an apostrophe 's' ('s) to the noun to signify possession.
In the given sentence, "Have you seen the mitten belonging to Margot?", the "mitten" which belongs to Margot can be changed to "Margot's mitten". This shows the ownership of the mittens.
Thus, the correct sentence becomes
"Have you seen Margot's mitten?"
