The incorrect statement(s) among (a) - (d) regarding acid rain is (are):
(a) It can corrode water pipes
(b) It can damage structures made up of stone.
(c) It cannot cause respiratory ailments in animals
(d) It is not harmful for trees

First, we recall what the term “acid rain’’ means. Rainwater whose pH is brought down below the normal value of about $$5.6$$ because of dissolved acidic oxides - mainly $$\text{SO}_2,\; \text{SO}_3,\; \text{NO}_2$$ - is called acid rain. The relevant chemical steps are:

$$\text{SO}_2 + \dfrac{1}{2}\,\text{O}_2 \;\longrightarrow\; \text{SO}_3$$

$$\text{SO}_3 + \text{H}_2\text{O} \;\longrightarrow\; \text{H}_2\text{SO}_4$$

$$2\,\text{NO}_2 + \text{H}_2\text{O} \;\longrightarrow\; \text{HNO}_3 + \text{HNO}_2$$

These strong acids dissolve in the rainwater and impart high acidity, which in turn produces well-known environmental effects. Now we analyse each given statement in the light of these facts.

Statement (a): “It can corrode water pipes.’’ Acids react with metals, and ordinary iron or steel water pipes undergo electro-chemical corrosion when continuously exposed to acidic water. Hence statement (a) is true; it is not incorrect.

Statement (b): “It can damage structures made up of stone.’’ Marble and limestone are mainly calcium carbonate, $$\text{CaCO}_3$$. The sulphuric and nitric acids present in acid rain react as

$$\text{CaCO}_3 + 2\,\text{H}^+ \;\longrightarrow\; \text{Ca}^{2+} + \text{H}_2\text{O} + \text{CO}_2$$

This reaction erodes the stone surface, leading to loss of shine, roughening and eventual disintegration. Therefore statement (b) is also true; it is not incorrect.

Statement (c): “It cannot cause respiratory ailments in animals.’’ The acidic aerosols and the precursor gases $$\text{SO}_2$$ and $$\text{NO}_x$$ irritate the mucous membranes of the nose, throat and lungs, aggravating asthma and bronchitis. Thus acid rain can cause respiratory ailments. The assertion that it “cannot’’ do so is false; therefore statement (c) is incorrect.

Statement (d): “It is not harmful for trees.’’ Acidic water leaches essential nutrients like $$\text{K}^+, \text{Ca}^{2+}, \text{Mg}^{2+}$$ from the soil and releases toxic aluminium ions, damaging roots and foliage. Consequently acid rain is indeed harmful to vegetation. Saying that it “is not harmful’’ is false; hence statement (d) is incorrect.

Summarising, the statements that are incorrect are $$ (c) \text{ and } (d) $$. Among the options provided, Option D lists exactly these two statements.

Hence, the correct answer is Option D.