Question 24

The atomic number represents the number of protons in an atom.

The atomic number is a fundamental property of an element that indicates the number of protons present in the nucleus of an atom. This number not only determines the identity of the element but also its position on the periodic table.

A) Number of neutrons

The number of neutrons in an atom is not represented by the atomic number; rather, it is a separate quantity that, when added to the number of protons, gives the atomic mass. Therefore, this option is incorrect.

B) Number of protons

This option correctly defines the atomic number, as it is specifically the count of protons in the nucleus of an atom that distinguishes one element from another. Each element has a unique atomic number, making this option the correct answer.

C) Number of electrons

While the number of electrons in a neutral atom typically equals the number of protons, the atomic number specifically refers to protons only. Therefore, this option is incorrect as it misrepresents the definition of atomic number.

D) Number of isotopes

The number of isotopes refers to the variations of an element that have the same number of protons but different numbers of neutrons. This concept is unrelated to the definition of atomic number, making this option incorrect.

Conclusion

The atomic number is accurately defined as the number of protons in an atom, which is essential for determining the element's identity. Options A, C, and D misinterpret or misrepresent the concept, thereby affirming that B is the only correct choice. Understanding atomic number is crucial for studying elements and their properties in chemistry.