Hey guys, in the past my chain would come off my front sprocket from time to time. I merely put the chain back on the sprocket and continued using my bike. However, it seems like the chain rub against the sprocket rather intensely, cutting away at the sprocket. Over time rust formed.

Firstly, did rust form because the sprocket is of cheap quality?

Secondly, can I clean and repair it?

As you can tell, I'm a cycling newb. Thanks for your help in advanced!