In one or two sentences, explain why the combined weight of several liquids mixed in an open flask can be less than but never more than the sum of all the weights of the ingredients.

The combined weights of several liquids mixed in an open flask be less than the sum of all the weights of the liquids because when the reaction occurs new products are formed and also some gases which releases in the atmosphere.

"the periodic table is arranged in order of atomic number."

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.

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