What does The letters in a chemical formula represent

the letters represent the atomic symbol of each atom. The subscript (lower) represents the number of each atom, while the superscript (higher) represents the charge on a given atom. A coefficient before a chemical formula represents that many units of the molecule.

indicate valleys, hills, steepness and gentleness of slopes.

explanation:

contour lines on a map indicate elevation, or depth. numeric notations on contour lines refer to the level of elevation, or height about sea level.