Classity each of the following as element, compound, or mixture

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

Which statement is usually true about the relationship between activation energy and reaction rates? low activation energy barriers result in low rates. high activation energy barriers result in low rates. low activation energy barriers result in no reaction. high activation energy barriers result in no reaction.

Can someone me with 3 and 4 plz. this is for masteries test.