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Multiple Choice
Which of the following materials is classified as a pure substance?
A
Brass
B
Air
C
Salt water
D
Oxygen gas (O_2)
Verified step by step guidance
1
Understand the definition of a pure substance: A pure substance has a fixed composition and distinct chemical properties. It can be either an element or a compound.
Analyze each option: Brass is an alloy (a mixture of metals), so it is not a pure substance.
Air is a mixture of gases (mainly nitrogen, oxygen, and others), so it is not a pure substance.
Salt water is a homogeneous mixture of salt (NaCl) dissolved in water (H_2O), so it is not a pure substance.
Oxygen gas (O_2) is a molecule consisting of only one type of element, oxygen, with a fixed composition, making it a pure substance.