What is the most toxic substance that accumulates in an aquarium?

Chen drew a diagram to compare the ways in which different organisms obtain nitrogen. which label belongs to the area marked z?

Apump contains 0.5 l of air at 203 kpa. you draw back on the piston of the pump, expanding the volume until the pressure reads 50.8 kpa. what is the new volume of the air pump

Why is retrograde motion an apparent motion