The quantity of protons in an element is identified by which of the following?

• A. Atomic mass
• B. Atomic number
• C. Molecular weight
• D. Isotope number

Answer: (B)

The quantity of protons in an element is defined by its atomic number. The atomic number is a fundamental characteristic of an element and is unique to each one. It represents the number of protons found in the nucleus of an atom of that element, and since the number of protons determines the identity of the element, the atomic number is a key identifier in the periodic table.

For instance, carbon has an atomic number of 6, which means it possesses 6 protons. This characteristic is critical because it plays a vital role in determining the chemical properties and behavior of the element. Other concepts, such as atomic mass, molecular weight, and isotope number, encompass different aspects of atomic structure or quantities but do not reflect the direct count of protons. Therefore, recognizing the atomic number is essential in understanding the properties and classification of elements.