Pentagon
an equilateral triangle
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.
octagon
Impossible.
An irregular quadrilateral.
The shape that has three lines of symmetry is the equilateral triangle. It also has three angles of equal size and three sides of equal length.
If your asking what shape has three lines of symmetry, your answer would be an equilateral triangle. You can tell how many lines of symmetry a shape that has all angles of the same measure has by looking at it's angles. Ex., pentagon has five angles--five lines of symmetry; octagon has eight angles, eight lines of symmetry; etc.
rhombus
a square
7
square and rectangles are technicality squares