The correct answer is nitrogen.
A layer of gases, generally known as air, which envelopes the planet Earth and is retained by the gravity of the Earth is called the atmosphere of the Earth. The dry air by volume comprises 78.09 % nitrogen, 0.93 % argon, 20.95 % oxygen, 0.04 % carbon dioxide, and smaller concentrations of other gases. Thus, when one is examining the quality of air in large cities, the element nitrogen should come about 80 percent in each of the samples of the air taken.
Vertical distance between contours is called contour interval
Contour lines are lines that connects point of equal height. The vertical distance or the difference in elevation between two contour lines is known as contour interval. For example a set of 100 contours is used to represent a hill of height 500 ft. So, the vertical distance between each contour will feet
ft contour interval.