The contour interval of a topographic map is 25 feet, and every fifth line is an index contour. what is the difference in elevation between index contours? a. 25 feet b. 100 feet c. 125 feet d. 175 feet

If the "contour interval" of a "topographic map" is 25 feet, and every fifth line is an index contour, the "difference in elevation" between index contours would be "125 feet".

Explanation:

A contour interval is defined as the fixed distance between any two contour lines plotted on the topography of a region. An index contour is a darker contour line drawn after every four contours for the convenience of reading the elevations. If the "contour interval" is fixed at 25 feet, the distance between two index contours would naturally be 125 feet.