Let’s examine both statements one by one and see whether they hold true for typical corrosion processes (e.g., iron rusting):

Statement (I)

"Corrosion is an electrochemical phenomenon in which pure metal acts as an anode and impure metal as a cathode."

Corrosion is electrochemical

True. Corrosion, especially rusting of iron, involves oxidation at one region (the anode) and reduction at another region (the cathode) on the metal’s surface.

Pure metal as anode, impurity as cathode

In many practical cases (e.g., iron containing small amounts of carbon or other impurities), the relatively pure region of the iron is more active (less noble) and tends to oxidize (lose electrons) — that is, it serves as the anode.

The impurity (e.g., carbon-rich region) often behaves more nobly and thus becomes the cathode region where reduction (e.g., oxygen reduction) occurs.

This difference in electrode potentials between the pure region and the impurity region drives the corrosion cell.

Hence, Statement (I) is generally considered true in the usual context of corrosion (like rusting of iron).

Statement (II)

"The rate of corrosion is more in alkaline medium than in acidic medium."

For most common metals (like iron), acidic media typically enhance corrosion because abundant H⁺ ions (and possibly other acidic species) can accelerate the oxidation/dissolution of the metal.

In mildly alkaline or neutral environments, metals often form protective oxide or hydroxide layers that can slow down further corrosion.

While certain strong bases can attack specific metals (e.g., Al in strong NaOH), in general for iron and many other metals, corrosion is more severe in acidic environments than in alkaline ones.

Thus, Statement (II) is false under normal corrosion scenarios (e.g., rusting of iron).

Conclusion

Statement (I): True

Statement (II): False

Therefore, the correct choice (matching these truth values) is:

(C) Statement I is true but Statement II is false.