Hi lawrence1234. Welcome to the forum.
For homework help you need to put this into the template. Also, you need to show that you have made some effort to solve your own problem. People here are not supposed to just do your homework for you. But I will give you some hints.
Problems of this nature are usually easier to solve if you look at the collision in the centre of momentum frame. In that frame the two particles will have equal but opposite momentum. In that frame an elastic collision is very simple. The particles come in with the same-but-opposite-sign momentum. They go out with same-but-opposite-sign momentum but in some other direction. But in this problem you don't know the angle they go out at. So you include this angle as a variable.
Then you transform the after-collision situation back to the lab frame and work out the possible angles the 2 kg particle could take. And find the maximum deflection.