Which one of the following elements can show both positive and negative oxidation state ?

The atomic size of Iodine is very big and it has empty d orbitals to expand it's electron in s and p orbitals In 3^rd excited state iodine has 7 unpaired electrons so it can show positive oxidation state with higher electronegative element like Cl, Br, F. Generally all halogens exhibit negative oxidation state due to their electronegativity.