Questions & Answers about De mist was rond de middag voorbij.
Because mist is a de-word in Dutch. Noun gender in Dutch is something you usually have to learn together with the noun.
So:
- de mist = the fog
There is no special reason visible from the form of the word here; it is just the correct article for this noun.
Rond de middag means around noon or around midday.
- rond = around
- de middag = noon / midday
It gives an approximate time, not an exact one. So the sentence does not mean the fog ended at one precise moment; it means this happened roughly around noon.