Is using a hot pack an example an example of an endothermic or exothermic

Arock can be broken down into different kinds of substances by physical processes. no chemical reactions are needed to separate different parts of a rock into pure substances. this is because a rock is a(n)

Often on a topographic map, every fifth contour line is darkened. what is this line called? a. key b.slope c.benchmark d. index contour

An atom of which element reacts with an atom of hydrogen to form a bond with the greatest degree of polarity ?