Element not showing variable oxidation state is :

Because of the absence of d-orbitals, it is not possible for Fluorine to show variable oxidation state. Fluorine does not show variable oxidation states because it is the most electronegative element and has seven valence electrons. Its high electronegativity and strong attraction for electrons prevent it from losing electrons to exhibit different oxidation states. Fluorine always show $-1$oxidation state in compounds. Fluorine does not show variable oxidation state.