Question

which of the following is an example of a pure substance?
a. salt
b. water
c. oxygen gas
d. all of these

Explanation:

A pure substance has a definite and constant composition. Salt (sodium - chloride) is a compound, water is a compound with a fixed ratio of hydrogen and oxygen, and oxygen gas is an element. All of them have a uniform and definite composition.

Answer:

D. all of these