The number of protons present in the nucleus of an atom of the element is called atomic number of the element. Since all atoms of a particular element have same number of protons in their nuclei, the atomic number of an element is characteristic of the element.
In 1913, Mosley introduced an atomic parameter called atomic number. Atomic number of an element is denoted by with, and can have only an integral value.
Mass number of an element is denoted by A. The mass number of an element is equal to the sum of the number of protons (P) and number of neutrons (N).
The first step or the problem in preparing the index numbers is the selection of the base year. The base year is defined as that year with reference to which the price changes in other years arc compared and expressed as percentages.