What metals aren't dissolved in/attacked by aqua regia?
Platinum, gold and mercury can be dissolved in aqua regia but iridium and silver cannot. Palladium and silver are, however, soluble in nitric acid. Ruthenium can be dissolved in aqua regia only when in the presence of oxygen (Why? will be asked in a separate question), while rhodium must be in a fine pulverized form. Niobium and …