What is a contour interval on a topographic map?

Contour intervals are the lines of equal elevations, separated by fixed amount, that helps in understanding the topography of an area within a map. when contour lines are narrow, it indicates a steep slope and when contour lines are broad, it indicates a broad or gentle slope. Contour line and map scale is inversely proportional to each other. This means that a small scale map generally shows larger contour lines, and a large scale map generally shows smaller contour lines.

Thus, contour lines while reading a map are the key features in identifying the hills and basins in a particular area.

c-14 is carbon-14, or radiocarbon.   it is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons.