Why is it important that the primary standard chemical be non-hygroscopic and pure? Why is it important to dry the primary standard to a constant weight?

It is extremely important for the primary standard chemical to be non – hygroscopic and pure and to also have a constant weight because you don't want any moisture or any impurities to alter the stoichiometric point in the 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.