The order of rotational symmetry of a 2D arrowhead shape is 1. This means that the shape can only be rotated about its center by 360 degrees to look the same, as it does not match its original position at any smaller angle. In other words, there are no other angles of rotation (like 90 or 180 degrees) that will make the arrowhead appear unchanged.
a circle.
A parallelogram
An irregular quadrilateral.
Septahedron
There is no such shape. A 2d shape with 5 sides and all equal angles must be a regular pentagon (or a 5-pointed star if you stretch the definition of "all angles"). And a regular pentagon - or star - has 5 lines of symmetry.
Regular polygon with any number of sides, circle, ellipse, isosceles triangle, rectangle, isosceles trapezium, kite, arrowhead.
A 2d shape with uncountable lines of symmetry is a circle.
The 2D shape which has one line of symmetry is the trapezium.
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Octagon
0
a circle.
A parallelogram
An isosceles triangle and a kite have only one line of symmetry.
a parallelogram, if it's 2d.
Square
A square