Mulching blades which this appears to be are hard tell if only slightly bent from looking at an image. If one is bent more than normal it will show up as you rotate it through a full rotate and seeing if one side lower than the other based on a reference point such as the edge of the mower deck. They also can be harder to sharpen correctly on some grinders.
Since you have hit something with it and these are usually fairly reasonable to replace or at they are here I think that be your best bet. You may even be able a better aftermarket blade cheaper than the OEM version. What I sell here to my customer is usually a little thicker and heat treated than the OEM blades. I don't what is available in your part of the world but a little research probably will payoff for you.
