Which statements are true about the periodic table? check all that apply. a. the periodic table is organized by atomic number. b. there are two different ways to number the groups of the periodic table. c. each box on the table represents one element. d. elements in the same row of the periodic table have the same number of electron shells.

Let's evaluate each answer closely:
A. The periodic table is organized by atomic number.
This statement is true the atomic number is what defines each element and is the number of protons and electrons in a neutral atom

B.There are two different ways to number the groups of the periodic table.
This is true.  The more modern method is to number the groups 1 - 18.  Earlier models used a Roman numeral and either an A or B to denote groups.
 
C.Each box on the table represents one element.
THis is also true.  Each box contains a unique element.

D.Elements in the same row of the periodic table have the same number of electron shells.
This is true.  The row that the element is on is also the number of electron shells that are in the element.