Questions & Answers about В салатнице лежат огурцы, помидоры и зелень.
Because в can mean either in or into, and the case shows which one it is.
- в + prepositional = location: в салатнице = in the salad bowl
- в + accusative = motion into something: в салатницу = into the salad bowl
Here the vegetables are already inside the bowl, so Russian uses the location form в салатнице.
They are in the nominative case, because they are the grammatical subject of the sentence — the things that лежат.
- огурцы = nominative plural
- помидоры = nominative plural
- зелень = nominative singular
Even though English may translate this part more flexibly, in Russian these words are simply the subject.