There are at most three right angles, because if all four right angles are 360, the fifth angle 180 degrees is impossible.

Suppose that four angles A, B, C and D in a Pentagon are acute angles,

Then the fifth angle e = 540-(a+b+c+d) > =540-4*90= 180

And because the angle e cannot be greater than 180 degrees,

So a Pentagon can't have four acute angles.

So at most three internal angles are acute angles.

There are at most five obtuse angles.