Which is true about periods and groups? O Groups are horizontal and their number tells us the number of energy levels in an atom of that
element. Periods are vertical and contain elements with similar properties.
Periods are horizontal and their number tells us the number of energy levels in an atom of that
element. Groups are vertical and contain elements with similar properties.

Periods are horizontal and their number tells us the number of energy levels in an atom of that  element.

Groups are vertical and contain elements with similar properties.

Explanation:

The periodic table systematically arranges elements over one another based on their atomic numbers.

Elements having the same number of electrons in the outermost shell of their atoms are placed over one another in vertical columns called groups or family. Hence, elements in the same group will have similar chemical properties.

Elements in the same period have the same number of electronic shell. This number corresponds to the energy level of the elements.

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first one is the correct answer