Inadequate risk assessment has the strongest negative impact when determining the scope of an audit engagement. This is because the scope sets the foundation and direction for the entire audit process. If risks are not properly identified and assessed at the beginning, the audit may focus on areas that are insignificant while neglecting critical areas, leading to an ineffective audit. In other phases like reviewing internal controls, testing, and evaluating findings, the auditor is already working within the predetermined scope. Hence, the most significant impact of inadequate risk assessment is at the scope determination phase.