Halogens are elements in Group 17 of the periodic table (Fluorine, Chlorine, Bromine, Iodine, Astatine). Let's examine each statement: a. They oxidize to form positive ions: While halogens are primarily known for gaining electrons, they can exhibit positive oxidation states (meaning they have been oxidized) when bonded to more electronegative elements, such as oxygen or fluorine. For example, in $\text{HClO}$, chlorine has an oxidation state of +1. In $\text{IF}_7$, iodine has an oxidation state of +7. So, they can* oxidize to form positive oxidation states. b. They are all non-metals: All halogens (F, Cl, Br, I, At) are classified as non-metals. This statement is correct. c. They oxidize to form univalent negative ions: This statement is incorrect. Halogens have 7 valence electrons and readily gain one electron to achieve a stable octet, forming univalent negative ions ($\text{X}^-$). The process of gaining electrons is called reduction, not oxidation. Therefore, halogens reduce to form univalent negative ions. The statement that they oxidize* to form negative ions is a contradiction of chemical definitions. d. They exist as diatomic molecules: In their elemental form, halogens exist as diatomic molecules ($\text{F}_2, \text{Cl}_2, \text{Br}_2, \text{I}_2$). This statement is correct. The question asks for the property that halogens possess except. Based on the analysis, statement c is fundamentally incorrect. The correct option is c. c) They oxidize to form univalent negative ions 3 done, 2 left today. You're making progress.