The property which is not true about fluorine is:
A.Most of its reaction are exothermic
B.It forms only one oxoacid
C.Highest electronegativity
D.Highest \[F - F\] bond dissociation enthalpy

Hint: To answer this question, you should recall the physical and chemical properties. Fluorine has atomic number 9 and has 7 valence electrons; it is highly reactive and electronegative.

Complete Step by step solution:
- Fluorine is a univalent poisonous gaseous halogen; it is pale yellow-green and it is the most chemically reactive and electronegative of all the elements. The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is known as electronegativity. It is a dimensionless property because it is only a tendency. We measure electronegativity on several scales. The most commonly used scale was designed by Linus Pauling.
- According to this scale, fluorine is the most electronegative element with a value of 4.0 and cesium is the least electronegative element with a value of \[0.7\]. Electronegativity decreases in a group on going from top to bottom. Therefore, increasing electronegativity order of halogens is \[I{\text{ }} < {\text{ }}Br{\text{ }} < {\text{ }}Cl{\text{ }} < {\text{ }}F.\]
- The element Fluorine is a poisonous gas. It usually exists as a fluoride ion in aqueous solution. It remains in the air for long when attached to tiny particles. The bond dissociation energy \[{\text{of F}} - {\text{F bond is }}{\mathbf{159}}{\text{ kJ/mol}}\] which is not high bond dissociation energy and it is because of the high electronegativity of fluorine atoms.

Thus, the correct answer to this question is option D.

Note: You should know Uses of Fluorine: Used in semiconductor manufacturing for plasma etching, MEMs fabrication, and flat panel display production. Chlorofluorocarbons are extensively used in air conditioners and refrigerators. Fluorides are also added to toothpaste to prevent dental cavities.