Final answer:
Chris would likely use contract law to sue Peter, specifically claiming an enforceable unilateral contract was breached when Peter refused to pay the $5,000 after Chris fulfilled the condition of not smoking.
Step-by-step explanation:
If Chris were to sue Peter, the most likely legal theory of recovery he would use is contract law, specifically under the basis of an enforceable unilateral contract. Since both parties agreed to the terms, and Chris upheld his end by refraining from smoking, he could argue that Peter's promise created a contract where Chris's performance was the consideration for Peter's promise of the $5,000.00 payment. Chris's legal action would be based on the premise that he fulfilled the required condition to receive the promised money, thus resulting in a breach of contract when Peter refused to pay. In this scenario, contract law generally supports the enforcement of such agreements where a clear offer, acceptance, and consideration are present, and the non-breaching party has performed the agreed-upon action.