The element that the business analyst should use to help the QA team validate that the product fulfilled the requirements without ambiguity is acceptance criteria. Acceptance criteria are statements that define the conditions that a product or feature must meet in order to be accepted by stakeholders or end users. They can help the QA team test the functionality based on specific scenarios or outcomes, and verify that it meets the expectations or needs of stakeholders or end users. Process maps are diagrams that show how a business process flows from start to end. They can help the QA team understand how a product or feature works in relation to a process, but not how to validate it without ambiguity. User stories are statements that capture a requirement or feature from an end user's perspective. They can help the QA team understand what needs to be done and why it matters, but not how to validate it without ambiguity. References:
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/user-stories
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/user-accepta