Which statement is a correct expression of the law of conservation of mass? a. the total mass is unpredictable in a chemical reaction. b. the total mass remains the same during a chemical reaction. c. the total mass decreases during a chemical reaction. d. the total mass increases in a chemical reaction.

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.

alchemy hadn't scientific methods of study, appeal to mysticism and fantasy, the knowledge of chemistry and physics were modest at that time.

alchemy was - but as new rules were discovered it either changed into chemistry or it became "unscientific".