The backdrop of the noble metals
Palladium, platinum, gold and mercury can be attenuated in aqua regia, a awful concentrated admixture of hydrochloric acerbic and nitric acid, but iridium and argent cannot. Argent is, however, acrid in authentic nitric acid. Ruthenium can be attenuated in aqua regia alone if in the attendance of oxygen, while rhodium accept to be in a accomplished burst form. Niobium and tantalum are aggressive to all acids, including aqua regia.
Other sources cover mercury,rhenium or chestnut as a noble metal. On the added hand, titanium, niobium, and tantalum are not included as noble metals, although they abnormally abide corrosion. noble metals should not be abashed with adored metals (although abounding noble metals accept top value).
While the noble metals tend to be admired – due to both their aberration in the Earth's band and their account in areas like metallurgy, top technology, and beautification (jewelry, art, angelic objects, etc.) – the agreement "noble metal" and "precious metal" are not synonymous.