The correct answer is option 3: Political Philosophy. The `Arthashastra` is a treatise written by the ancient Indian scholar Kautilya, also known as Chanakya. It is one of the oldest and most comprehensive texts on political science and governance. The text covers a wide range of subjects related to statecraft, including politics, administration, diplomacy, economics, military strategy, and law.

Option 1: Economics - While the `Arthashastra` does discuss economic principles and policies, it is not solely focused on economics. It provides a holistic view of governance and covers various aspects of statecraft.

Option 2: Environment - The `Arthashastra` does not specifically discuss the environment or environmental issues. Its main focus is on the organization and functioning of the state.

Option 4: Religion in Administration - Although religion and religious practices are briefly mentioned in the `Arthashastra`, the text primarily focuses on political philosophy and the practical aspects of governance. It provides guidelines for rulers, administrators, and leaders on how to effectively govern a kingdom or state.

In summary, the `Arthashastra` is a treatise on political philosophy, encompassing a wide range of topics related to governance and statecraft.