Breakdown of На празднике будет около десяти гостей.
Questions & Answers about На празднике будет около десяти гостей.
Because на празднике answers the question where? — at the party / at the celebration.
After на when it means location, Russian uses the prepositional case:
- на празднике = at the party
By contrast, на праздник would usually mean for the party or to the party depending on context, not at the party.
So here:
- На празднике будет... = At the party, there will be...
With many events, Russian idiomatically uses на to mean at:
- на концерте = at the concert
- на уроке = at the lesson/class
- на встрече = at the meeting
- на празднике = at the celebration/party
So this is mostly something you learn as a normal collocation:
- быть на празднике = to be at the party
В празднике would sound more like in the celebration in a more abstract sense, not the normal way to say someone is physically attending the event.