Elements of Groups 16, 17 and 18

They have ns²np⁵ configuration, They are called salt-forming elements, They are highly reactive, They exist as diatomic molecules

Halogens have ns²np⁵ configuration, are called salt-forming elements (Greek: halo=salt, gene=born), are highly reactive due to high electronegativity, and exist as X₂ molecules. Except F, others show multiple oxidation states.

Small atomic size, High electronegativity, Absence of d-orbitals

Oxygen's anomalous behavior is due to its small size, highest electronegativity after fluorine, and absence of d-orbitals in valence shell which prevents expansion of octet.

ClO₂

Chlorine dioxide (ClO₂) is used as a bleaching agent for paper pulp and textiles due to its strong oxidizing properties without damaging the material.

Angular

Ozone has angular (bent) structure with O-O-O bond angle of about 117°. It is a resonance hybrid of two canonical forms.