It's better if you shared your approach.
Looks like balancing torque for the rod
It should lose contact at that point(normal=0)
Write force eq at that instant to find eq1)
Then it follows parabola path.For it to reach diametrically opposite point it should have that point in its trajectory.While solving that equations we get value of theta)
Then substitute in eq 1)to get ans.
If you have any doubts pls do ask
When I checked soln they have given a shorter method by taking diameter as reference line.
In my soln I have taken vertical as ref line
Ty @Bhuvanitha_2020, can u plz upload the solution pdf. I had just got the question paper from somewhere....
Check out this thread