Conservation of mass to balance the following reaction. Na2S+ KI= NaI+ K2S

Iknow #2 is d. i just need to know why

Explain that newton first law,second law and third law of motion?

Clyde and marilyn are riding a roller coaster. during which section(s) of the track is their potential energy converted to kinetic energy? a. from point b to point c only b. from point b to point d only c. from point a to point b only d. from point a to point b and from point c to point d