MCQ Detailed View

Atoms are the basic building blocks of matter, consisting of three main particles: protons, neutrons, and electrons. A neutral atom is one in which the number of positively charged protons is exactly balanced by an equal number of negatively charged electrons, resulting in no overall electric charge.

The atomic number of an element is defined as the number of protons in its nucleus. Since a neutral atom has an equal number of protons and electrons, the atomic number directly tells us the number of electrons in that atom. For example:

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  Hydrogen: Atomic number = 1 → Electrons = 1

  
  


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  Carbon: Atomic number = 6 → Electrons = 6

  
  


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  Oxygen: Atomic number = 8 → Electrons = 8

  
  

The atomic weight (or mass number) represents the sum of protons and neutrons in the nucleus. It cannot be used to determine the number of electrons because neutrons do not affect the electric charge of the atom.

Similarly, the number of orbitals refers to the available energy levels or regions around the nucleus where electrons may be found, but it does not specify how many electrons are actually present. The electron count is always dictated by the atomic number for a neutral atom.

Understanding this concept is fundamental in atomic physics and chemistry, as electron count determines an element's chemical properties, bonding behavior, and placement in the periodic table.

Thus, the correct answer is Atomic number, as it gives a direct and automatic way to know the number of electrons in a neutral atom.