Both aluminium and zinc react with dilute hydrochloric acid to liberate H$_2$ gas, but aluminium reacts faster. Which factor affecting reaction rate does this illustrate?

1. The two metals are compared under the same conditions of size, concentration and temperature. 2. Only their chemical nature differs: Al is more reactive than Zn, so Al reacts faster. 3. This shows that the reactivity, i.e. the nature of the reactants, influences the rate. 4. Particle size, concentration and temperature are kept comparable here, so those factors are not the answer. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 3 "Chemical Reactions and Equations", p.49_