2 - University prom
3 - Kitchen clock
What you need to remember, generally, about possessives is that they denote exactly that - possession. A kitchen is a room in your house. It cannot really "possess" anything. The clock does not belong to the kitchen. The kitchen does not possess or own the clock.
A kitchen clock is a clock which is designed to be hung/stood in the kitchen.
"My mother's kitchen clock is blue" - I am not telling you that there is a blue clock which belongs to my mother's kitchen. I am telling you that there is a blue kitchen clock which belongs to my mother.
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