Hij is jaloers op zijn collega. (He is jealous of his colleague.)
jaloers takes "op" (jaloers op = jealous of). Example: Hij is jaloers op zijn collega. (He is jealous of his colleague.)
Hij is jaloers op zijn collega. — He is jealous of his colleague. 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.