Never
sometimes
Sometimes
sometimes
Sometimes
sometimes
sometimes
If they are congruent they must be similar.
"Congruent" means "same shape and size as the other one". So one thing all by itself is never congruent. It needs something else to be congruent with. An isosceles triangle is never congruent to a scalene triangle, sometimes congruent to any other kind of triangle, and always congruent to another isosceles triangle that's congruent to the first one.
Sometimes.
Sometimes similar but it depends
sometimes, the altitude of isosceles triangles resting on their base and equilateral triangles are angle bisectors
They are sometime congruent because a square is a parallelogram and its sides are congruent and a rectangle is one and its sides aren't congruent.