All the atoms of elements listed in each row of the periodic table have the same number of

electron shells

Explanation:

A period in the periodic table is a row of chemical elements. All elements in a period have have the same number of electron shells. Electrons in the atom are arranged in shells, the first shell allows 2 electrons, so if more electrons are present, a second shell is needed. The second shell allows 8 electrons, so if there are present more than 10 electrons, a third shell is needed (notice that 2 electrons go to the first level and 8 to second one). This reasoning is repeated for every other levels. All the atoms of elements listed in each row of the periodic table have the same number of electron shells.

the answer is b, encourage free trade

answer; primary source information;