What do you mean by 925 silver plated ring?
“925” is sterling silver, an alloy that is 92.5% prata. If you see 925 stamped on an item, it means that it’s solid sterling silver. Nothing else. In America I believe it is illegal to use a 925 stamp for anything that is not solid sterling (silversmiths feel free to correct me if that is wrong) If you go to a reputable jeweler, that’s the only thing that will be stamped 925. Silver plated rings will not be stamped 925.
No entanto, the jewelry market has recently been flooded with items that aren’t solid sterling, but have the 925 mark anyway. Manufacturers in China are apparently putting the stamp on just about anything that looks like silver, as a marketing device. The item could be plated with sterling. It could be plated with something that is silver in color, but not actually made of silver at all. You have no way to know. If you ask the vendors of such items if they are solid sterling, you may get an evasive answer like “it is marked 925 sterling.” Well, yeah, it’s marked. But in some parts of the world that has no meaning; it’s just an advertising scam.
I have numerous “925 silver plated” items from China that do not have a gram of real silver in them, anywhere. Most are copper, coated in a shiny silver alloy. I also have a few steel and copper chains plated in genuine silver. Real silver plate only has a microscopically thin layer of real silver, so if an item looks it was dipped in thick silver paint, that ain’t the real thing.
So if what you are looking at is called “925 sterling”, and it is from a part of the world where the 925 mark is being misused, it might have some sterling silver on it or not. You have no way to know.
925 Silver tarnishes, and imitation silver alloys don’t, so in time you’ll figure it out.
As an example, here is the online listing for an item I ordered from China. I tested it when it arrived and found the core was copper, and the plating was some non-silver alloy. Below are the specs.
Shiny Findings 925 Sterling Silver Fashion Jewelry DIY Making Accessory 2 PCS/1Pair Earring Hoop
Earring hook
Convertion: 1 mm=0.039 inch, 1 inch=25.4 mm
Material:925 Prata de lei
Quantities: 2 PCS/1 Pair
Diameter: 0.9cm
Width: 0.15cm
Height: 1.1cm