Gold is a rare metallic element with a melting point of 1064 degrees centigrade and a boiling point of 2808 degrees centigrade. Its chemical symbol, Au, is short for the Latin word for gold, 'Aurum', which literally means 'Glowing Dawn'. It has several properties that have made it very useful to mankind over the years, notably its excellent conductive properties and its inability to react with water or oxygen.
This stems back to ancient times in the Mediterranean /Middle East, when a carat became used as a measure of the purity of gold alloys (see next Question 5). The purity of gold is now measured also in terms of fineness, i.e parts per thousand. Thus 22 carat is 22/24th of 1000 parts = 916 fineness.
A Carat (Karat in USA & Germany) was originally a unit of mass (weight) based on the Carob seed or bean used by ancient merchants in the Middle East. The Carob seed is from the Carob or locust bean tree. The carat is still used as such for the weight of gem stones (1 carat is about 200 mg). For gold, it has come to be used for measuring the purity of gold where pure gold is defined as 24 carats.
Pure Gold is yellow in colour, but when alloyed with other metals, results in varying colours of Gold. Gold alloys are usually a mixture of Silver, copper, and zinc, where the amounts of each vary depending on the desired final colour, normally white and red Gold.
Hallmarking on a piece of Gold jewellery will give you an indication of where it was manufactured. However, hallmarking is only a legal requirement in some countries, such as the United Kingdom. While in other countries it may be done voluntarily, sometimes it is not carried out at all. In places where hallmarking is carried out, small symbols on the item ascribe information such as caratage, country of manufacture and the company that manufactured it. The amount of the information available from the hallmark will vary according to the standards of the country that the jewellery was purchased in.
BIS is a regulatory body of the Govt. of India which has standardized various products consumed today. It is extremely crucial to understand the benefits provided by ensuring Hallmark Jewellery. BIS certified gold Hallmarked Jewellery can be identified by 5 visible marks on the back of the jewellery – a BIS mandate. These are:

BIS Hallmark LogoPurity of Gold '916' -22ct, '875' - 21ct etc.The Hallmarking centre's logo The jewelers' identification markYear of Hallmarking 'A' -year 2000, 'B' -year 2001 .... 'T’ – year 2015.
No, it is quite different. White Gold achieves its whiteness when other metals are added to yellow Gold. Platinum, conversely, is white to begin with and maintains its luster permanently. Since white Gold is really yellow Gold with alloys added to it, the alloys tend to wear away with usage. To keep your white Gold jewelry looking its best, you can have it polished and rhodium plated on a regular basis.