What is Precious Metal?

A Precious Metal is a metal with rare metallic chemical element and due to that is of high economic value. Precious metals are less reactive than most elements, have high luster, and have higher melting points than other metals. Gold, Platinum and Silver are considered as p recious metals and used extensively in jewelry

What is the Silver jewlery mark 925?
Silver 925 is great for jewelry because it is flexible and highly reflective. However, it is also soft and prone to losing its shape with extensive wear. To strengthen the soft metal and enhance its suitability for jewelry, it is mixed it with other metals to create an alloy (92.5% silver and 7.5% other metals, mostly copper) . That's why the silver jewelry has 925 mark. 
How does sterling silver differ from silver plated?
Silver plated items are made from a very thin coating of pure silver over other metals. When the coating of silver flakes or scrapes off, the base metal underneath is revealed. Sterling silver, which contains much more silver, is an alloy (mixture) so it is bonded much more tightly to the other metals and does not flake off. Since it is a mixture instead of a coating, it will be a consistent color throughout the piece. So if it were to get scratched, the underlying color would be the same color as the outer layer and would be much less noticable than a scratch on a silver plated piece.