Question

which sample is a pure substance?
o zinc oxide
o sugar dissolved in water
o pond water
o soil

Explanation:

A pure substance has a definite and constant composition. Zinc oxide is a compound with a fixed chemical formula (ZnO). Sugar dissolved in water is a solution (a mixture). Pond water contains various dissolved substances, organisms etc., and is a mixture. Soil is a heterogeneous mixture of minerals, organic matter etc.

Answer:

zinc oxide