(a) Biomagnification — Accumulation of chemicals at the successive trophic levels of a food chain

(b) Ecosystem — Biotic components of environment

(c) Aquarium — A man-made ecosystem

(d) Parasites — Organisms which obtain food from other living organisms

Solution –  the mismatched pair in the above combinations is the –

Ecosystem — Biotic components of environment

The correct combination would be Ecosystem – consists of biotic and abiotic components of the environment