Sales Ops department has noticed that the Sales Reps are converting a lot of the unqualified leads. The department wants to change the process and ensure specific information is being entered before the sales rep does any lead conversion. Which Salesforce feature will allow Sales Ops to handle this issue better?

Answer options:

A.Formula Fields
B.Workflow Rule
C.Duplicate Rules
D.Validation Rules

Correct Answer: D 
Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record. A validation rule can contain a formula or expression that evaluates the data in one or more fields and returns a value of True or False. Validation rules also include an error message to display to the user when the rule returns a value of True due to an invalid value. 
Option A is incorrect because formula fields are read-only field and its value is evaluated from the formula or expression defined by us. 
Option B is incorrect because the workflow rule automates certain business processes. You can create a rule based on certain criteria that you set. 
Option C is incorrect because duplicate rules define what happens when a user views a record with duplicates or starts creating a duplicate record. 
References: 

https://help.salesforce.com/articleView?id=fields_defining_field_validation_rules.htm&type=5

Correct Answer: D 
Validation rules verify that the data a user enters in a record meets the standards you specify before the user can save the record. A validation rule can contain a formula or expression that evaluates the data in one or more fields and returns a value of True or False. Validation rules also include an error message to display to the user when the rule returns a value of True due to an invalid value. 
Option A is incorrect because formula fields are read-only field and its value is evaluated from the formula or expression defined by us. 
Option B is incorrect because the workflow rule automates certain business processes. You can create a rule based on certain criteria that you set. 
Option C is incorrect because duplicate rules define what happens when a user views a record with duplicates or starts creating a duplicate record. 
References: 

https://help.salesforce.com/articleView?id=fields_managing_field_validation.htm&type=5