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Multiple Choice
Which of the following substances is classified as a compound?
A
O_2
B
Fe
C
NaCl
D
Air
Verified step by step guidance
1
Step 1: Understand the definitions of elements, compounds, and mixtures. An element consists of only one type of atom, a compound consists of two or more different atoms chemically bonded together, and a mixture contains two or more substances physically combined but not chemically bonded.
Step 2: Analyze each substance given: O_2 is a molecule made of two oxygen atoms (same element), so it is an element in molecular form.
Step 3: Fe is a pure element, iron, consisting of only one type of atom.
Step 4: NaCl consists of sodium (Na) and chlorine (Cl) atoms chemically bonded together in a fixed ratio, making it a compound.
Step 5: Air is a mixture of different gases (mainly nitrogen, oxygen, and others) physically combined, not chemically bonded, so it is a mixture, not a compound.