Explanation:

✅ D. All of the above
To validate data migration accuracy and completeness, a comprehensive approach leveraging multiple tools is essential. Each option contributes uniquely to ensuring data integrity, consistency, and adherence to requirements post-migration. Salesforce Reports and Dashboards provide high-level comparisons to identify discrepancies, Data Compare tools like Informatica PowerCenter offer detailed record-level analysis, and Validation Rules enforce data quality within Salesforce. Using all these tools together ensures a thorough validation process, covering visualization, detailed analysis, and compliance with data standards, minimizing the risk of errors or missing data.

❌ A. Salesforce Reports and Dashboards providing data comparisons between legacy and Salesforce systems
While Salesforce Reports and Dashboards are valuable for visualizing and comparing data between legacy and Salesforce systems, they primarily offer high-level insights. They may not catch granular discrepancies at the record or field level, nor do they enforce data formats or constraints. This makes them a critical part of the validation process but insufficient on their own for ensuring complete accuracy and completeness.

❌ B. Data Compare tools like Informatica PowerCenter analyzing record discrepancies and data integrity
Data Compare tools like Informatica PowerCenter excel at identifying record-level discrepancies and ensuring data integrity through detailed analysis. However, they focus on technical comparisons and may not provide user-friendly visualizations or enforce ongoing data quality within Salesforce. Without complementary tools like reports or validation rules, these tools alone cannot address all aspects of migration validation.

❌ C. Validation Rules on key fields within Salesforce ensuring data adherence to defined formats and constraints
Validation Rules in Salesforce are crucial for enforcing data quality by ensuring fields meet specific formats and constraints post-migration. However, they are reactive, only addressing data entered or updated in Salesforce, and do not compare legacy system data or provide insights into discrepancies. They are an important component but not comprehensive enough without comparison and analysis tools.

Reference:
Salesforce Validation Rules