Final answer:
Elements in the modern Periodic Table are placed in increasing order of their a. atomic number.
Step-by-step explanation:
The modern Periodic Table arranges elements in increasing order of their atomic number. The atomic number represents the number of protons in the nucleus of an atom. Chemists use the atomic number to organize elements in the Periodic Table because it helps to determine an element's properties and its position in the table. For example, hydrogen, with an atomic number of 1, is the first element in the table, while oxygen, with an atomic number of 8, is in the second period.