Taking SCARY out of used bikes, one bike at a time.
Chainrings do wear out. When the chain stretches and there has been a lot of hard riding on one gear it will round the teeth. This will cause the chain to skip under load. So if this happens to you check those chainrings and you can replace them in most cases.
To find the right chain ring, you need the bolt pattern messure, how many speeds and teeth count. If you miss any of these you will have the wrong chainring. If you drop by your local shop they should be able to tell you what you are looking for.