Explanation
A validation rule is a tool that allows administrators to enforce data quality and integrity by preventing users from saving records that do not meet certain criteria or conditions. For example, a validation rule can display an error message if a user enters an invalid value in a field. In this case, the administrator can create a validation rule on the account object that displays an error if the account annual revenue field is below 0 or greater than 100 billion. References:
https://help.salesforce.com/s/articleView?id=sf.validation_rules.htm&type=5

Explanation
Contact, lead, and person account are three objects that will have the individual field available for tracking data privacy information when data protection and privacy is enabled for an org. The individual object is an object that stores data privacy preferences and requests for customers who are subject to privacy regulations such as GDPR; it can be linked to contact, lead, or person account records using the individual field. Case and opportunity, account and user, or individual, user, and account are not combinations of objects that will have the individual field available for tracking data privacy information; they either do not store customer data or do not support individual object relationships. References:
https://help.salesforce.com/s/articleView?id=sf.individual_object.htm&type=5

Explanation
To require the Amount field during the negotiation stage for sales users but allow their managers to make changes, the administrator should configure a validation rule that checks if the user profile is not a sales manager, the stage is negotiation, and the amount is blank. This will prevent sales users from saving the record without entering an amount, but allow sales managers to do so. Making the field required for all users will not meet the requirement. Creating a formula field or assigning the administrator profile to the managers will not affect field requirement. References:
https://help.salesforce.com/s/articleView?id=sf.validation_rules_overview.htm&type=5

Explanation
To track all cases that reference the new product and give read/write access to the product's two lead engineers, the administrator should create a queue and a criteria-based sharing rule. The queue will allow assigning cases that meet certain criteria, such as having a specific value in the Product field, to a group of users. The criteria-based sharing rule will grant read/write access to the queue members for cases that match the same criteria. References: https://help.salesforce.com/s/articleView?id=sf.queues_overview.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.sharing_criteria.htm&type=5

Explanation
Validation rules allow you to prevent users from changing an opportunity close date to a date in the past.
References: https://help.salesforce.com/s/articleView?id=sf.validation_rules.htm&type=5