Iridium is one of the most corrosion-resistant metals: it resists almost all acids, aqua regia, molten metals, and even silicates at high temperatures. But some molten salts, such as sodium cyanide and potassium cyanide, as well as oxygen and halogens (especially fluorine), can still attack iridium at high temperatures.
combined state

The oxidation states of iridium compounds range from −3 to +6, the most common being +3 and +4. Compounds with high oxidation states are relatively rare, including IrF6 and two mixed oxides, Sr2MgIrO6 and Sr2CaIrO6. In 2009, scientists used matrix isolation (in 6K argon) to UV-irradiate iridium peroxide complexes to make four Iridium oxide (IrO4). However, this compound is not expected to remain stable in a solid state at higher temperatures.
Iridium has the second highest density of all elements, only slightly lower than osmium. Since the density values are so similar and measurement is not easy, which of the two elements has the higher density has never been conclusive.