Explanation:

- Option 1: Reserve the state treasury

- An officer managing the state treasury would be responsible for the safekeeping and regulation of funds.

- Option 2: Tax assessment

- The Samaharta was indeed responsible for tax collection and assessment according to ancient Indian texts like the Arthashastra. This officer played a crucial role in the financial administration of the kingdom.

- Option 3: Security assurance

- This would typically refer to an officer handling the safety and defense of a region or state, which was not the role of the Samaharta.

- Option 4: To correspond

- This involves communicating or managing correspondence, which would not align with the primary duties of a Samaharta.