Arrange the following elements in order of increasing (from smallest to largest) atomic size: H, Br, Cl, O. Explain the reasoning behind your chosen order.

Explanation:

Atomic size is defined as the distance between the nucleus and valence shell of an atom. Valence shell is the outermost shell of an atom.

When we move across a period in a periodic table then there will occur a decrease in atomic size of the atoms. But when we move across a group in a periodic table then there will occur an increase in atomic size of the atom.

Hydrogen is a period 1 element, oxygen is a period 2 element, chlorine is a period 3 element and bromine is a period 4 element.

Therefore, given elements are arranged in order of increasing atomic size as follows.

                             H < O < Cl < Br