Final answer:
Isolation is a step in the Containment phase of Incident Response, critical for preventing the spread of threats after a security incident.
Step-by-step explanation:
In the field of Incident Response within IT security, isolation is a critical step that pertains to the containment phase. It involves disconnecting or limiting access to the infected systems and falls under the CompTIA's IRP category. When a security incident is detected, isolating the affected systems or network segments is crucial to prevent the spread of the threat and mitigate potential damage. Isolating the system could involve disconnecting it from the network, limiting its network access, or physically removing it from the network.
This step is considered to be part of the Incident Response procedures as dictated by the CompTIA Security+ guidelines, more specifically under the category of IRP (Incident Response Procedure). Therefore, so, the correct option is the Incident Response Procedure within the CompTIA categories for assigning isolation.