Final answer:
The WHERE clause is used to apply a filter based on a condition in Proc SQL.
Step-by-step explanation:
The correct clause to apply a filter based on a condition in Proc SQL is the WHERE clause. It is used to specify the criteria for the records you want to retrieve from a table. For example:
SELECT * FROM table_name WHERE condition;
Here, condition represents the specific condition or criterion you want to apply as a filter.