50 points! hydrogen gas and oxygen gas are combined to form water (h2 + o2 → h2o). is this a chemical change or a physical change? explain your answer.

Chemical change, because the atoms are being rearranged and we get a new substance.

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: