yes
no they dont
In general, a square. A square always has 4 lines of symmetry. A pentagon need not have any. Only a regular pentagon can have 5 lines of symmetry. But if you created pentagons from sides with random lengths then, assuming the pentagons existed, only a tiny fraction would be regular: most pentagons would have no axes of symmetry.
triangles
A square has four; a pentagon has five.
This depends on the type of prism. If the shapes on the ends are pentagons, the prism has 6 planes of symmetry. If they are hexagons, it has 13 planes of symmetry. It has the same number of planes of symmetry as the shapes on the end have lines of symmetry, plus 1.
A regular pentagon has five lines of symmetry, but a specific type of pentagon known as an irregular pentagon can have only two lines of symmetry. An example would be a pentagon where two sides are equal in length, and the angles opposite these sides are equal, creating reflectional symmetry across those two lines. However, the specific arrangement would affect the overall symmetry, so not all irregular pentagons will have exactly two lines of symmetry.
Not if they are regular 5 sided pentagons
regular pentagons have no parrallel lines. irregular pentagons might but it depends. :))
If you're talking about convex polygons with equal sides (eg. equilateral triangles, squares, pentagons, hexagons, etc.), then the relationship is a very direct one. In those cases, there are as many lines of symmetry as there are points in the polygons. A triangle has three lines of symmetry, a square has four, a pentagon five, etc.
2 lines of symmetry
The square is the only one I can think of. The lines are vertical, horizontal, and both diagonals.
A nephroid has 2 lines of symmetry.