The purity of silver is expressed in India with the help of BIS marks which can in terms of fineness which can go as high as 99.99% purity (BIS 999.9). There are three BIS grades for fine silver which are BIS 999.9 (99.99% purity), BIS 999.5 (99.95% purity), BIS 999 (99.9% purity). But they are usually sold only as coins or bars which can be bought in most jewellery stores in your city. You only need to check the BIS hallmark to verify the purity of purchase.
If you are looking for pure silver jewellery or silver articles though, they usually only have a purity as per BIS standards of 970, 925, 900 etc. This means that 97-90% of the metal by mass in the jewellery would be silver and the rest would be other metals. Other metals are mixed to make the silver alloy, so as to make the silver jewellery less soft and more durable.