The correct answer is A (Consequence) because, according to CCPS Risk-Based Process Safety (RBPS) principles, risk is defined as a function of both likelihood (or frequency) and consequence (severity) . This relationship is fundamental to hazard identification and risk analysis methodologies such as HAZOP, LOPA, and quantitative risk assessment (QRA).

Likelihood represents how often an event may occur, while consequence reflects the potential impact of that event, including effects on people, environment, assets, and business. A high-risk scenario typically involves either a high likelihood, severe consequences, or both.

Option B (Probability) and D (Frequency) are closely related to likelihood and therefore do not complete the definition—they are essentially components of the same side of the risk equation. C (Safeguards) are measures used to reduce either likelihood or consequence but are not part of the definition of risk itself.

CCPS emphasizes that effective risk management requires evaluating both dimensions. For example, even a low-probability event may require strong controls if the consequences are catastrophic. This dual consideration supports prioritization of hazards and the design of appropriate layers of protection to reduce overall risk to tolerable levels.