Option 1 suggests that stratospheric ozone and chlorofluorocarbons (CFCs) are the cause of potential damage to the Taj Mahal. However, these elements generally harm the earth`s ozone layer and do not directly cause damage to monuments.

Option 2 is the correct answer. The emissions from the oil refinery and thermal power plants could result in acid precipitation (also known as acid rain) and increased levels of tropospheric ozone. Both elements can cause corrosion and decay of the monument`s white marble.

Option 3 involves the greenhouse effect caused by rising CO2 levels. While this could potentially cause global warming and broader climate change, it is unlikely to directly affect the structure or material of the Taj Mahal.

Option 4 suggests that ultraviolet radiation and pollution from the Yamuna river are the cause. While these factors could have environmental consequences, they are not primarily responsible for the potential threat to the Taj Mahal`s structure from an oil refinery or thermal power plants.