Which of the following is MOST helpful in determining the effectiveness of an organization's IT...

Key risk indicators (KRIs) are metrics that provide information about the level of exposure to a specific risk or a group of risks.

Reviewing KRIs is the most helpful way to determine the effectiveness of an organization’s IT risk mitigation efforts. This means that the organization monitors and evaluates the actual results and outcomes of the risk responses, compares them with the risk appetite and tolerance of the organization, identifies any deviations or breaches that may require attention or action, and reports them to the appropriate parties for decision making or improvement actions.

The other options are not the most helpful ways to determine the effectiveness of an organization’s IT risk mitigation efforts. They are either secondary or not essential for risk management.

The references for this answer are:

Risk IT Framework, page 15

Information Technology & Security, page 9

Risk Scenarios Starter Pack, page 7