The arrangement of elements in the Modem Periodic Table is based on their

increasing atomic number in the horizontal rows

The correct answer is option 2. increasing atomic number in the horizontal rows.

The arrangement of elements in the Modern Periodic Table is based on their increasing atomic number in the horizontal rows. This means that as you move from left to right across a period (horizontal row), the atomic number of the elements increases. This arrangement was proposed by Henry Moseley, who discovered that elements' properties were better organized by atomic number rather than atomic mass. Therefore, the periodic table is organized such that elements with similar chemical properties fall into the same vertical columns (groups), with atomic numbers increasing from left to right across each row (period).