Which reaction will occur?
2nabr + i2 mc023-1.jpg 2nai + br2
2fe + al2o3 mc023-2.jpg 2al + fe2o3
2agno3 + ni mc023-3.jpg ni(no3)2 + 2ag
pb + zn(c2h3o2)2 mc023-4.jpg zn + pb(c2h3o2)2

Only the third reaction will occur:
2AgNO3 + Ni = Ni(NO3)2 + 2Ag. The more active metal Ni replace less active metal Ag from the salt.
The first reaction is impossible, because iodide can't replace bromide from the salt
The second reaction is impossible, because Fe is less active metal than Al.
The last reaction is also impossible, because Pb is less active metal than Zn.

Elias is almost correct. he just got it backwards.the correct answer is that it demonstrates elastic potential energy transforming into kinetic energy.