Sometimes they are.
sometimes
Parallelograms are squares is sometimes true. Squares are parallelograms is always true. Rhomboids are parallelograms is also always true. So not all parallelograms are squares but some are.
sometimes
sometimes
Sometimes similar but it depends
Never
Sometimes.
never ever ever
If they are congruent they must be similar.
If they have the same nuber of sides (angles) then always. If not then never. So, overall, I suppose the answer is sometimes - depending on the number of sides.
Circles are congruent when they have the same radius and they are similar when their radii are different in lengths.