Answer: the answer is B
Explanation: I just took the quiz :)
Their combined momentum after they meet is 0 .
Car is moving on the glassy slope with constant speed
Now we know that

so acceleration is rate of change in velocity
as we know that velocity is constant here so acceleration is zero
so here

now as we know by Newton's II law

since a = 0

so net force will be ZERO on it during this motion
Since they are made of different chemical make ups, boiling point and density they will most likely be in different groups on the periodic table.