Which statements about the structure of the periodic table are true?

the periodic table has an irregular shape because it has more periods than groups.
the inner transition elements are placed at the bottom of the periodic table for easy viewing.
the periodic table has horizontal groups and vertical periods, giving it a regular rectangle shape.
the distribution of electrons in energy levels is responsible for the shape of the periodic table.
nonmetals take up more than half the area of the periodic table.

The distribution of electrons in energy levels is responsible for the shape of the periodic table.

Explanation:

Henry Moseley in the 1900s re-stated the periodic law by changing the basis of the table to reflect more on the atomic number. The present law is therefore "the properties of elements are a periodic function of their atomic numbers".

Atomic number is the number of electrons in an atom and it is the same as the number of protons for neutral atoms.

In the table, elements having the same number of electrons in the outermost shell of their atoms are placed over one another in vertical columns. Each of the vertical column is known as a group or family while each of the resulting horizontal rows is known as period or row.