For a given launch velocity, at which launch angle does the projectile undergo the maximum horizontal displacement

45°

Explanation:

The horizontal displacement of any projectile (assuming the it is launched from the same height as it arrives) is given by:

As you can see it depends on both the sine and cosine of the launch angle.

When you graph that multiplication (cos(α) * sin(α)), you can see that it has a maximum peak at (shown in the picture)

You could also derive the expression and find its maximum but I'll leave that for another time.

the awnser is d you right bro