Why are the atomic masses of most of the elements not whole numbers ?

Are the atomic masses of some elements actually fractional ?

Atomic mass of an element is not neccessurity a whole number because

Why are atomic masses regarded as relative masses?

Atomic mass of an element is

An element is found in nature in two isotopic forms with mass numbers (A-1) and (A+3). If the average atomic mass of the element is found to be A, then the relative abundance of the heavier isotope in the nature will be :

If the atomic number of an element X is 17, then what will be the atomic number of the element lying in the same group as that of X but in the fifth period?

Which of the following properties of an element is a whole number ?

Complete the following sentences : (a) The mass number and atomic number of an element are not changed when it emits …………………. (b) The atomic number of a radioactive element is not changed when it emits …………………………… (c ) During the emission of a beta particle, the ................. number remains same.

State the relation between atomic number and atomic mass for light elements. State which elements are considered radioactive giving reasons.

Statement-I : Mass numbers of most of the elements are fractional. Because Statemen-II Mass numbers are obtained by comparing with the mass number of carbon taken as 12.