Moving from left to right across a row of the periodic table, which of the following values increases by exactly one from element to element?
a. isotope number
b. atomic number
c. atomic mass unit
d. mass number

The periodic table is an arrangement of the chemical elements found in nature. These elements are ordered by their atomic number, the configuration of their electrons as well as their chemical properties.

The current periodic table has 115 elements listed in 7 periods and 10 groups.
Moving from from left to right across a row of the periodic table, the atomic number increases by exactly one from element to element.