객관식
How many electrons can the second energy level of an atom hold?
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2. Atoms & Elements
The Atom
객관식
Which of the following is the atomic number of helium?
A
4
B
1
C
2
D
6
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검증된 단계별 안내1
Recall that the atomic number of an element is the number of protons in the nucleus of an atom of that element.
Identify helium on the periodic table, which is the second element in the noble gases group.
Note that helium has 2 protons in its nucleus, which means its atomic number is 2.
Understand that the atomic mass (approximately 4 for helium) is different from the atomic number; atomic mass counts protons plus neutrons.
Therefore, the correct atomic number for helium is 2, distinguishing it from the other numbers given.
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