Q.Arrange the order of increasing atomic volumes in:

Atomic radius is the distance from an atom's nucleus to the outermost shell holding a valence electron. Since it cannot be measured for an isolated atom, it is reported as a covalent radius (half the bond length between two identical, singly covalently bonded atoms, e.g. $r_{Cl} = 0.99$ Angstrom from the 1.98 Angstrom Cl2 bond length) or a metallic radius (half the distance between adjacent atoms in a metallic lattice, e.g. $r_{Cu} = 1.28$ Angstrom).

Across a period, atomic radius decreases: successive valence electrons enter the same shell while the nuclear charge keeps growing (one more proton per element), so the increasing effective nuclear charge (see Effective Nuclear Charge and Slater's Rules) pulls the valence shell in tighter at every step. …