ANS:B - number

Atomic number of an element is a whole number. Explanation: The atomic number of an element represents the number of protons in the nucleus of an atom of that element. It is a fundamental property of an element and is denoted by the symbol "Z." Each element on the periodic table has a unique atomic number. Since the atomic number corresponds to the number of protons, which are fundamental particles with a unit positive charge, it is always a whole number. Atomic weight, on the other hand, represents the average mass of the atoms of an element, considering all its isotopes and their relative abundances. Atomic weight may not always be a whole number because it accounts for the presence of isotopes with different masses. Atomic volume and atomic radius also relate to atomic properties but do not necessarily have to be whole numbers. They represent measures of the size or volume of an atom, which can vary depending on the atomic structure and bonding characteristics of the element.