A square or a rectangle
Right angle.
square
The circle is the reflex angle, the square means it's a right angle.
right angle square
Square.
A square and a rectangle
A square.
a right angle or a 90 degree angle, the sides are perpendicular to each other
If the question is about only one right angle, then the answer is a kite, arrowhead or a miscellaneous quadrangle which has no specific name.
It could be a kite, an arrowhead or an irregular quadrilateral with a right angle - which has no specific name.
a square