Question 3
Why does the rate of reaction rise as the concentration rises?
The right answer is the one marked above.
The number of reactant particles in unit volume goes up, and so does the number of collisions in unit time. Concentration is by definition the number of particles in unit volume.
It is temperature, not concentration, that raises the kinetic energy. The surface area does not change either — all three pieces of magnesium ribbon have the same surface area.