Can x and y axis have different scales? In a graph on reflection, can i give the x axis a scale of 4 cms = 10 degrees , and the y-axis a scale of 2 cms = 10 degrees? Will it affect the readings? 
 A: I'm guessing from your question that you're fairly new at this game (I've been doing it for nearly 40 years! :-).
Actually it's usually the case that the x and y scales are different because we're usually graphing different things. In your case you're graphing angles against angles, but graphs might be distance against time or force againt distance or lots of things that have different x and y axes.
So choose whatever scales make the graph look clearest. Just be a bit careful when you're measuring the gradient: make sure you allow for the difference in scale. From looking at your quesion in the Math Exchange I think you already know this.
Response to comment: remember what the point of a graph is. It's a visual aid that allows you to quickly judge by eye what the relationship between two sets of data looks like. Few of would actually measure things off a graph these days, we'd just feed the data into some computer program and let it chew on it. But before you press Enter it's a good idea to have a feel for what the data looks like, and that's where the graph comes in.
Generally speaking when you draw a graph you're looking for straight lines. You don't say what your experiment is, but if you're reflecting light from a mirror the graph of incident angle against reflected angle will be a straight line. The angle of the straight line will change if you change the scales, but that's all right because all you're really interested in is whether the line is straight or not.
Actually, from your question I wonder if you meant refraction not reflection. With reflection the incident and reflected angles are always equal so the graph looks a bit boring and you wouldn't need different scales. If you did mean refraction then your graph isn't going to be a straight line (especially at large angles). In that case it's possible to get a straight line but you have to graph something slightly different.
