Amoving object undergoes an acceleration when it's blank or blank changes

Observe that the object below moves in the positive direction with a changing velocity. An object which moves in the positive direction has a positive velocity. If the object is slowing down then its acceleration vector is directed in the opposite direction as its motion (in this case, a negative acceleration).

31 protons

37 Neutrons

^68 Ga

Explanation:

I don’t know the second part, but I’m guessing 37 because 37+31=68