(1) Prepositions confuse me, too -- especially in, on, for, to.
(2) I think that I am correct in saying that at would not be
(3) I think that (at least in the United States), this is the usual practice:
(a) Use on if you are referring to your apartment balcony:
They were eating on the balcony.
(b) Use in if you are referring to a balcony in a theater:
There are a few available seats in the balcony.
Let's see what others say.
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