Questions & Answers about После пикника мы соберём мусор в парке.
Because после requires the genitive case.
- пикник = nominative dictionary form
- после пикника = after the picnic
For masculine nouns like пикник, the genitive singular often ends in -а or -я, so:
- пикник → пикника
This is very common:
- после урока = after the lesson
- после работы = after work
- после фильма = after the movie
Соберём is the future tense of the perfective verb собрать.
Here the idea is we will collect it / we will finish collecting it, so Russian uses a perfective future form.
- собирать = imperfective, process/habit
- собрать = perfective, completed result
Compare:
- Мы собираем мусор. = We are collecting garbage / We collect garbage.
- Мы соберём мусор. = We will collect the garbage.
So соберём fits because the sentence refers to a future completed action after the picnic.