Answer:
b. Chief Legislator.
Step-by-step explanation:
An act is first passed in the Congress to make it to the desk of the President. After it is passed by Congress, the act reaches the President's office to be signed into law.
In this case, as given in the question, the Environment Act that Congress passed is sent to the President's desk. After reviewing the act, if the President signs the bill, it becomes a law. And in the process of signing the act into law, the President is acting as the Chief Legislator of the law.
Thus, the correct answer is option b.