Which of the following halogens doesn't exhibit positive oxidation state in its compounds?
For this, we need to know the tendency of an element to gain or lose electrons.
We know electronegativity is the tendency of an atom to attract a bond pair of electrons. F is the most electronegative element among all the elements known to us, i.e., it prefers to gain rather than lose electrons to other elements and no other element is capable of gaining an electron from F.
Hence F does not show positive oxidation states in any of its compounds.