Thermal power plants can lead to:

We start by recalling that a thermal power plant works by burning large quantities of fossil fuels such as coal, oil or natural gas. The combustion of these fuels inevitably releases flue-gases that contain pollutants, mainly $$\text{SO}_2$$ (sulphur dioxide) and $$\text{NO}_x$$ (a collective symbol for nitric oxide $$\text{NO}$$ and nitrogen dioxide $$\text{NO}_2$$).

Once these acidic oxides enter the atmosphere, they undergo a sequence of chemical reactions in the presence of moisture and oxygen. The key reactions are

$$\text{SO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_3$$

$$2\,\text{SO}_2 + \text{O}_2 \rightarrow 2\,\text{SO}_3$$

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

and, for nitrogen oxides,

$$2\,\text{NO}_2 + \text{H}_2\text{O} \rightarrow \text{HNO}_2 + \text{HNO}_3$$.

The resulting acids—sulphurous acid $$\text{H}_2\text{SO}_3$$, sulphuric acid $$\text{H}_2\text{SO}_4$$, nitrous acid $$\text{HNO}_2$$ and nitric acid $$\text{HNO}_3$$—mix with cloud droplets. When these droplets fall to the ground as rain or snow, the precipitation has a pH value significantly lower than normal, a phenomenon commonly called acid rain.

Now we compare this effect with the four options given in the question:

A. Acid rain — exactly matches the process described above; thermal power plants are a major anthropogenic source of this problem.

B. Blue baby syndrome — caused by high nitrate concentrations in drinking water, typically due to agricultural runoff, not by emissions from thermal power plants.

C. Ozone layer depletion — primarily linked to chlorofluorocarbons (CFCs) and related halogenated compounds, again not associated with thermal power plant emissions.

D. Eutrophication — the excessive enrichment of water bodies with nutrients (especially phosphates and nitrates) leading to algal blooms; this is more related to agricultural and sewage discharges than to thermal power plants.

Therefore, only option A corresponds to a direct environmental consequence of thermal power plant operation.

Hence, the correct answer is Option A.