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Multiple Choice
In the classification of matter, which of the following is NOT a compound?
A
B
C
D
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Verified step by step guidance
1
Step 1: Understand the definition of a compound. A compound is a substance formed when two or more different elements chemically bond together in fixed proportions.
Step 2: Examine each given substance to determine if it is a compound. For example, \(\mathrm{H_2O}\) (water) consists of hydrogen and oxygen atoms chemically bonded, so it is a compound.
Step 3: Check \(\mathrm{NaCl}\) (sodium chloride), which is made of sodium and chlorine atoms bonded together, so it is also a compound.
Step 4: Look at \(\mathrm{CO_2}\) (carbon dioxide), which contains carbon and oxygen atoms chemically bonded, making it a compound as well.
Step 5: Identify \(\mathrm{He}\) (helium). Helium is a single element and exists as individual atoms, not bonded to other elements, so it is not a compound but a pure element (a noble gas).