One of the important factor on which rate of reaction depends is surface area. That is, when a compound is crushed into powdered form then there will be increase in surface area of the compound.
Hence, now more number of particles can interact, therefore, there will be increase in rate of reaction.
Thus, we can conclude that reaction occurs more quickly when powdered iron is used instead of a single piece of iron of the same mass because the powdered iron has a greater surface area than the single piece of iron.
The answer is (3). The powdered iron and the piece iron is the same substance and is just different in the shape. So the reason is the power has larger surface area for reaction occurs.
Chemical compounds are any substance composed of identical molecules consisting of atoms of two or more chemical elements. So NO2 and KBr are compounds, Br2 and Fe are not.
