The INCORRECT statement is:

We begin by recalling some basic facts about common engineering alloys. An alloy is a homogeneous mixture of two or more metals (or a metal and a non-metal) whose overall properties differ from those of its constituents. Knowing the standard compositions allows us to test each statement one by one.

First, let us examine bronze. By definition, bronze is the mixture $$\text{Cu} + \text{Sn}$$, that is, copper combined with tin. Because this matches the wording “bronze is an alloy of copper and tin,” we see that statement A is factually correct.

Next, we consider cast iron and wrought iron. Industrially, cast iron contains a relatively high percentage of carbon (about $$2.0 \%$$ to $$4.5 \%$$). To obtain wrought iron, which has a very low carbon content (usually $$\lt 0.1 \%$$), cast iron is subjected to a refining process known as puddling or an equivalent decarburisation step. Hence, the route $$\text{cast iron} \longrightarrow \text{wrought iron}$$ is indeed standard practice, so statement B is also correct.

Now let us look at german silver, also called nickel silver. Its usual composition is approximately $$\text{Cu} : 60\% ,\; \text{Zn} : 20\% ,\; \text{Ni} : 20\%.$$ Thus it truly is an alloy of zinc, copper and nickel, and statement C agrees with this fact.

Finally, we evaluate brass. Textbook metallurgy tells us that brass is the binary alloy $$\text{Cu} + \text{Zn}$$ (copper and zinc). There is no nickel in ordinary brass; alloys of copper and nickel are instead called cupro-nickel or nickel silver (distinct from brass). Therefore the claim that “brass is an alloy of copper and nickel” is erroneous.

Summarising, statements A, B and C are correct, while statement D is incorrect.

Hence, the correct answer is Option D.