Answer:
a condition subsequent.
Step-by-step explanation:
Based on the scenario being described within the question it can be said that this clause is known as a condition subsequent. This refers to an event or state of affairs that causes something else to come to a close, usually being an individuals legal rights or duties that come to an end. Which in this case if the condition is met in this scenario then it would cause Jack to retrieve the right to sell the frozen food himself.