Question

how are elements arranged on the periodic table of elements?
a by electron configuration
b by atomic number
c by valence electrons
d by atomic mass

Explanation:

Elements in the periodic table are arranged in order of increasing atomic number. The atomic number represents the number of protons in an atom's nucleus and determines the element's identity. Electron - configuration and valence electrons are related to an element's position in the table but are not the basis of the overall arrangement. Atomic mass does not determine the order of elements in the periodic table.

Answer:

B. by atomic number