"Are there people at the bank?"
Translation:В банку є люди?
It plays a role of "there is" in English. It's really tricky since we skip it all the time in other cases...
- Люди в банку -- Люди (є) в банку (є is usually skipped) = The people are in the bank.
- В банку люди = В банку є люди (both are equally common) = There are people in the bank.
So it depends on the word order apart from having or not having "є".
Different words decline differently depending on the gender and the type of the ending.
Typically, for masculine in Locative the ending is -і if the noun ends with "softer" kinds of consonants. From my native speaker perspective, those consonants are easily softened by -і. For example, ні is very easy to pronounce, the н sounds soft like the Spanish ñ. But кі is hard and uncomfortable to pronounce, the softening of к is not so smooth.
So for example, these endings tend to have -і in Locative: -ж (на ножі), -з (у розрізі), -л (на столі), -м (у храмі), -н (у стані), -п (в окропі), -р (на дворі), -с (у лісі), -т (на капоті but в аеропорту). And all of the consonants are more or less easily softened.
The harder ones tend to have -у: -д (у саду, but for example also, у комоді), -к (у банку), -х (на даху).
As you can see, д and т are unclear, as their soft forms are quite OK. To be fair I myself had to search whether it's "в аеропорті" or "в аеропорту". I don't say this word often, so I forgot the form; and it sounds equally OK to me (so like, the neural network in my brain which decides what sounds natural and OK couldn't decide)
So, there is kind of a pattern, with some exceptions, I'm not entirely sure as I'm just basing this explanation on my feeling :) I couldn't find any "official" explanation so far.