The answer for Part A is: In an action-reaction pair the forces work on different objects.
Its is already a balanced equation so the option a.1 would fill in for the blank.
B and C
When particles get colder and lose energy, they begin to move less and less. Gas particles move the most, with solid particles moving the least. So, it makes sense that if the substance loses energy and gets colder, it will also transform from gaseous state to liquid state since the particles are also moving slower as a result of it losing energy.
Hope this helped!
