Explanation:

The Modern Periodic Table organizes elements based on their atomic number, electron configuration, and recurring chemical properties. In this arrangement, elements are placed in horizontal rows and vertical columns. The horizontal rows are known as Periods. There are 7 periods in the periodic table, and elements within the same period have the same number of electron shells. Option B (Group) refers to the vertical columns, where elements share similar chemical properties due to having the same number of valence electrons. Option C (Blocks) refers to the classification of elements based on their highest energy electron orbital (s-block, p-block, d-block, f-block). Option D (Segments) is not a standard term used in periodic table nomenclature. Hence, horizontal rows are called Periods.