Answer:
The correct answer is: 'increasing atomic number'.
Step-by-step explanation:
In the modern periodic table the elements are arranged in increasing order of their atomic numbers.An atomic number of an element represents the number of protons present in the nucleus of an atom of that element.
In modern periodic table elements are placed in 18 groups that is vertical columns and in 7 periods that is horizontal rows.
The element ins same group has similar chemical properties. Where as elements in same period has same number of energy levels or shells.