Platinum is the 78th element on the periodic table. It's one of the least reactive metals since it does not oxidize even at its melting point of 1768.3 °C. It's so unreactive it can the corrosion of most acids. It has a very high density of 21450 kg per cubic metre.
Due to its unreactive properties, platinum is used for making electrodes for electrolyzing very corrosive substances.
Platinum is often used as a catalyst and can trigger many chemical reactions easily. Thus, it and Rhodium are used for making catalytic converters in car exhausts, which turn hazardous exhaust gases such as carbon monoxide into less hazardous substances such as Carbon dioxide.
Platinum has lots of different applications, but it is extremely hard to obtain since 1 kg of it costs up to USD$30 000. Thus, it is also used for making jewellery. But surprisingly Platinum is still cheaper than gold which can cost as much as $50 000 per kilogram.