Periodic table contains how many periods A. 6 B. 7 C. 8 D. 10

The periodic table contains 7 periods. A period is a horizontal row in the periodic table. The elements in a period have the same number of electron shells. The first period contains only two elements, hydrogen and helium. The second period contains eight elements, lithium through neon. The third period contains eight elements, sodium through argon. The fourth period contains eighteen elements, potassium through krypton. The fifth period contains eighteen elements, rubidium through xenon. The sixth period contains thirtytwo elements, cesium through radon. The seventh period is incomplete and contains only eighteen elements, francium through