Question

The long form of the periodic table is based on:
A) Number of electrons.
B) Mass of the atoms.
C) Electronegativity.
D) Shape of the atom.

Answer 1

Hint: In chemistry, Periodic table is the organized array of all the chemical elements which are arranged by atomic number, electron configuration, and recurring chemical properties. The arrangement of periodic tables leads to visualize the certain trends among the atoms.

Complete answer:
There are several rows and columns in the periodic table in which elements are arranged according to their properties.
The seven rows of table are called periods and generally have metals on left and nonmetals on the right. The columns are known as groups that contain elements with the similar chemical behaviors. Each element has a unique atomic number that represents the number of the protons in its nucleus. Most of the elements differ in numbers of neutrons among the same atoms and these are called isotopes.
The periodic table shows all the elements and their physical properties and it is arranged on the basis of atomic numbers and electron configurations of the elements. On the basis of atomic number, periodic table made. Atomic number is equal to the number of electrons.

Thus, the correct answer is A. i.e., Number of electrons.

Additional Information: In the periodic table, the elements are arranged in order of increasing atomic number. A new row (period) is started when the new electron shell has its first electron. Columns (groups) are determined by electron configuration of an atom.

Note: The scientist who brought it all together was a Russian chemist i.e., Dmitri Mendeleev. In 1869, he started the development of periodic tables, arranging chemical elements by atomic mass. He predicted the discovery of the other elements, and left spaces open in the periodic table for them.