Explanation:

Correct Answer is (a).There is error in the bold part of the sentence and that is why it needs to be replaced by the correct phrase. If we go through the bold part of the sentence, it is talking about the plans of the government but actually we are referring to a particular plan of the government only i.e. the decision to increase the tax on the petroleum product. Therefore, ‘the plan’ should have been used in this context.
The correct sentence would be:
The political leaders have gone to meet the President to protest against the plan of the government to increase the taxes on the petroleum products.This makes option A the correct choice among the given options.