Question

Which of the following correctly describes atomic number?

A) the atomic number is the number of atoms in a mole of a given substance

B) the atomic number is the number of neutrons in an atom

C) the atomic number is the number of atoms in a gram of a given substance

D) the atomic number is the number of protons in an atom

Answer 1

The atomic number is the number of protons in an atom, which defines the identity of the element.

Step-by-step explanation:

The atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. It is the defining trait of an element, as it determines the identity of the atom. For example, carbon has an atomic number of 6, which means it has 6 protons. In a neutral atom, the number of protons is equal to the number of electrons. The total number of protons and neutrons in an atom is called its mass number (A), and the number of neutrons can be calculated by subtracting the atomic number from the mass number: A - Z = number of neutrons.