Your Answer :
☆ I looked in the cupboard for the cat's food. (Singular)
☆ What is you brothers' favorite movie? (Singular)
☆ Did you find the boys' hiding place? (Plural)
☆ Today is Ms. Mill's birthday. (Singular)
☆ Are you the group's new president? (Plural)
What is Possessive Nouns :
A possessive noun is a noun that shows possession or belonging.
How to identify it ?
It generally includes an's for a singular person possessing one or more persons, places, or things, called a singular possessive noun and an s' for more than one person possessing singular or plural persons, places, or thing.
~ Benjemin360