In TCP/IP networking, the ACK flag is used to acknowledge the receipt of a packet. It's a way to confirm that the previous packets have been received and that the connection is proceeding as expected. The RST flag, on the other hand, is used to reset the connection. It is sent if a segment arrives which is not intended for the current connection, or if a connection request is to be denied. Essentially, the ACK flag is about maintaining the established connection, while the RST flag is about aborting connections that are not valid or are no longer needed123.

The weaponization step in the Cyber Kill Chain Model involves the creation or use of a specific weapon (malware, exploit) designed to leverage a vulnerability.
This phase follows the reconnaissance phase where the attacker gathers information and precedes the delivery phase where the weapon is delivered to the target.
Developing specific malware to exploit a vulnerable server is a precise example of weaponization.
Reference:
Lockheed Martin Cyber Kill Chain Model
Understanding the Weaponization Phase in Cyber Attacks
Steps in the Cyber Kill Chain

Encryption allows the user to make the data incomprehensible without a specific key, certificate, or password.
Encryption is a method of transforming data into a format that only authorized parties can access. Encryption can be used to protect data in transit or at rest from unauthorized access or modification. References:
https://learningnetworkstore.cisco.com/on-demand-e-learning/understanding-cisco-cybersecurity-operations-fund (Module 4, Lesson 4.1.1)