Q: What is the atomic number?


Read this paragraph and choose the correct option from the provided answers:

In the modern periodic table, elements are organized by atomic number. The atomic number is the number of protons in an atom of an element. This number is unique for each element, so it seems like an obvious way to organize the elements. (Mendeleev used atomic mass instead of atomic number because protons had not yet been discovered when he made his table. ) In the modern table, atomic number increases from left to right across each period. It also increases from top to bottom within each group. How is this like Mendeleev’s table?.

 Choices:

- Number of electrons

- Speed of electrons

- Number of neutrons

- number of protons


A:
number of protons