An experiment is performed in which a crystalline substance is added to a beaker filled with room temperature water. The following observations are made: I. The crystals dissolve

II. A precipitate is formed.

III. The bottom of the beaker feels warm to the touch.

IV. Bubbles begin forming within the water.

All of the observations are evidence of a chemical change EXCEPT -

Group of answer choices

I.

II.

III.

IV.

Hot air balloons float in the air because of the difference in density between cold and hot air. in this problem, you will estimate the minimum temperature the gas inside the balloon needs to be, for it to take off. to do this, use the following variables and make these assumptions: the combined weight of the pilot basket together with that of the balloon fabric and other equipment is w. the volume of the hot air inside the balloon when it is inflated is v. the absolute temperature of the hot air at the bottom of the balloon is th (where th> tc). the absolute temperature of the cold air outside the balloon is tc and its density is ďc. the balloon is open at the bottom, so that the pressure inside and outside the balloon is the same. as always, treat air as an ideal gas. use g for the magnitude of the acceleration due to gravity.

Which of the following electromagnetic waves can create ions?

Which of the following are sources of revenue for media companies? a. direct sales to producers b.advertising and subscriptions c. online purchase d. capital investments