I'm confused with some prepositions and google doesn't help so I would be grateful if someone could help me.

Please help me with the below, i'm interested in prepositions in bolid, which are possible? are there more than one possibility? if so, than which are more common?

1. the Christmas tree is on/in/at Trafalgar Square.
2. it stands on/in the apex of a rectangle.
3. try the booth at/in/on Trafalgar Square
4. throw it to/on the roof
5. you see sth in the tree but apples are on the tree?
6 10 o'clock on/in my watch

thank you
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Comments  (Page 2) 
1.the Christmas tree is at Trafalgar Square.

2.it stands on the apex of a rectangle.

3.try the booth on Trafalgar Square .

4.throw it on the roof .

5.you see sth on the tree but apples are in the tree.

10 o'clock in my watch .