Which of the following substances is made up of only one kind of atom? A. Iron

B. Salt

C. Steel

D. Water

it's option A. Iron (it's a pure substance containing only Fe²+ or only Fe³+)

Explanation:

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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.