Equiangular (not eqiangular) polygons are equiangular. These can be, but need not be, regular polygons.
Each of the 3 interior angles measure 60 degrees
Yes, they can be equal and that is called an equilateral triangle. It is also eqiangular.
rhombus
rectangle
Yes because to be similar the shapes need to have the same ratio of sides and similar angles. To be congruent the shapes have to be the same shape and size, so 2 congruent shapes will always be similar.
Quadrilaterals are shapes that always have four (4) sides
your ball sack
Yes and it is always at the exact middle between the shapes
The following is the answer.
a rectangle
An irregular polygon
A square.