What are the higher oxidation state and lower oxidation states of halogens according to inert pair effect?

The inert pair effect refers to the tendency of the outermost s electrons (the inert pair) to remain unshared in the process of chemical bonding. This effect is more prominent in heavier elements of the p-block, such as halogens.

1. Lower Oxidation States of Halogens: The lower oxidation states of halogens are -1. This is because halogens have seven valence electrons and they need one more electron to complete their octet. Therefore, they usually form -1 ions.

2. Higher Oxidation States of Halogens: The higher oxidation states of halogens can be +1, +3, +5, and +7. This is due to the fact that halogens can use their vacant d orbitals to expand their octet and show these higher oxidation states. However, the stability of these higher oxidation states decreases down the group due to the inert pair effect. For example, Fluorine (F) shows only -1 oxidation state, but Iodine (I) can show +1, +3, +5, and +7 oxidation states.

So, according to the inert pair effect, the lower oxidation state of halogens is -1 and the higher oxidation states can be +1, +3, +5, and +7.