The correct answer is: A) Periods form horizontal rows; groups form vertical columns.
Explanation: In the periodic table, elements are arranged in a specific order based on their atomic number, and this arrangement creates distinct periods and groups. Periods are the horizontal rows of the periodic table, and as you move from left to right across a period, the atomic number increases. Each period corresponds to the highest energy level of electrons in the elements within that row.
On the other hand, groups are the vertical columns in the periodic table. Elements within the same group share similar chemical properties and have the same number of valence electrons, which influences their reactivity and bonding behavior. So, the statement that periods form horizontal rows and groups form vertical columns is indeed true.