Find the volume of the figure. A rectangular prism is shown. The length is labeled 5 meters. The width is labeled 10 meters. The height is labeled 2 meters. Enter the correct answer in the box.

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.