Hint: Atomic size, atomic radii, atomic number, weight are all the properties of an atom. These are different for atoms of different elements. The atoms of the same element will have the same properties.
Complete answer: Atomic size of an atom is the distance between the centre of the nucleus of an atom and its outermost shell. In other words, it is the shortest distance between the atom’s nuclei and the outermost shell of the atom. A similar concept to atomic size is atomic radius or atomic radii. It is defined as half the distance between adjacent atoms of the same element in a molecule.
Additional Information: When two atoms are combined, then we can estimate their atomic size by checking the distance between the atoms. The atomic size of a non-metallic element is measured by forming a single covalent bond between two atoms and checking the distance between the two atoms. The radius found by this method is known as the covalent radii of the element. In the case of metal, it is termed as a metallic radius. The Atomic radius of an atom is measured by X-ray or other spectroscopy methods. In the periodic table, the atomic radii of elements vary in a fixed pattern. The atomic radius decreases as we move from left to right in a period and it increases when we go down a group.
Note: Students should learn the difference between the atomic size and atomic radii carefully. Both the concepts might seem similar in early observation but are very different fundamentally. Measurement of atomic radii is a complicated process and therefore, one should consider them an approximate value which is precise to the true value. There might be a little bit of error always present in them.