According to the PMBOK® Guide, the process responsible for prioritizing individual project risks is Perform Qualitative Risk Analysis.

Risk Prioritization: This process assesses the priority of identified risks by evaluating their probability of occurrence and their corresponding impact on project objectives (such as schedule, cost, or quality).

Tools Used: The primary tool used is the Probability and Impact Matrix. By plotting risks on this matrix, the project manager can categorize them as high, medium, or low priority.

Subjective Assessment: Unlike quantitative analysis, qualitative analysis is usually performed quickly and cost-effectively. It relies on the perceptions of the project team and stakeholders to determine which risks require the most immediate attention or further analysis.

Output: The key output is an updated Risk Register, where risks are now ranked or prioritized. This allows the team to focus their limited resources on the most " critical " threats and opportunities.

Why other options are incorrect:

Option B: Perform Quantitative Risk Analysis: This process uses numerical analysis (like Monte Carlo simulations) to quantify the combined effect of risks on project objectives. While it provides deeper data, it is usually performed after qualitative analysis and only on the risks that have already been prioritized.

Option C: Plan Risk Responses: This process focuses on developing options and actions to enhance opportunities and reduce threats. You must know the priority of the risks (from Qualitative Analysis) before you can effectively plan how to respond to them.

Option D: Implement Risk Responses: This is the execution phase where the agreed-upon risk response plans are put into action. It does not involve the initial ranking or prioritization of the risks themselves.