The oxidation state, also known as oxidation number, of an atom in a chemical compound indicates the degree of oxidation (loss of electrons) or reduction (gain of electrons) that the atom has undergone. It’s a way to describe the distribution of electrons in a molecule and is crucial for understanding the chemical behavior of compounds.

Here are a few key points about oxidation states:

1. Oxidation State Rules: Assigning oxidation states involves a set of rules. Some general guidelines include:
   • The oxidation state of an element in its elemental form is always 0.
   • In most compounds, oxygen is assigned an oxidation state of -2 and hydrogen is assigned +1.
   • The sum of oxidation states in a neutral compound is equal to 0, and in a polyatomic ion, it’s equal to the ion’s charge.
2. Oxidation States in Compounds: The oxidation state of an atom can be determined by considering the electronegativity difference between the atoms in the compound and how the electrons are likely to be shared or transferred.
3. Transition Metals: Transition metals, like iridium, can exhibit multiple oxidation states due to the availability of d orbitals for electron distribution. The oxidation state of a transition metal can vary in different compounds.
4. Examples: In iridium(III) chloride (IrCl3​), iridium is in the +3 oxidation state, meaning it has lost three electrons and has a positive charge of +3. In iridium hexafluoride ($IrF6$)—although it is a hypothetical compound—Iridium would likely have an oxidation state of +6 since fluorine typically has an oxidation state of -1.
5. Importance: Oxidation states are crucial for understanding redox reactions, predicting chemical reactivity, and balancing chemical equations.

Please note that while the general principles of oxidation states remain consistent, there might be some exceptions and special cases in specific compounds.