Option 1: This is incorrect because while it is true that coal-based thermal power stations contribute to acid rain, and oxides of carbon are emitted when coal burns, the latter isn`t the cause of the former. The oxides causing acid rain are sulphur dioxide and nitrogen oxides, not carbon oxides.

Option 2: This is the correct answer. Both the assertion and the reason are true statements. Coal-based thermal power stations do contribute to acid rain. However, the explanation provided in the reason is false because the emission contributing to acid rain from burning coal isn`t the carbon oxides, but rather sulphur dioxide and nitrogen oxides.

Option 3: This is incorrect. While the assertion is true, the reason isn`t false; it`s simply not the correct explanation of the assertion.

Option 4: This is also incorrect. Although the reason is true, the assertion isn`t false, hence invalidating this option.