Assigning information risk to a department without designating an individual owner is most likely to have a negative impact on accountability for information risk ownership. This lack of individual accountability can lead to ambiguities in responsibility, making it difficult to ensure that appropriate risk management actions are taken and followed up on. When an individual owner is clearly identified, it establishes direct responsibility and accountability, improving the effectiveness of risk management practices. While the scenarios described in the other options present challenges, the absence of a specific individual owner represents a fundamental weakness in establishing clear accountability for managing information risk.