>>965335>Does the chain ring it needs replacingIt's getting there but maybe not quite yet. If you replace the chain then you might want to though.
Compare it to pic related.
>is there a standard for chain ring mountingIt's called BCD - Bolt Circle Diameter? It's the distance between the bolts (that's what you measure anyway), you'll need to match it. It can be slightly tricky because it's easy to measure the wrong thing, so LBSs often get it wrong. Be cautious.
http://www.sheldonbrown.com/cribsheet-bcd.html