Er is kans op regen. (There is a chance of rain.)
kans takes "op" (kans op = chance of). Example: Er is kans op regen. (There is a chance of rain.)
Er is kans op regen. — There is a chance of rain. The preposition op is fixed, so it doesn't change with the sentence.
Fixed prepositions come up all over the A2 exam. The platform drills them in real exam tasks, AI-graded across all five DUO sections.