Final answer:
The most likely factor to prevent a valid S corporation election is being a foreign corporation, as S corporations must be domestic entities. While timely filing and shareholder requirements are also important, the late filing can be remedied, and there are exceptions for fiscal years.
Step-by-step explanation:
The most likely factor to prevent a valid S corporation election is c. Being a foreign corporation. For a corporation to be eligible for S corporation status, it must meet certain requirements as per the Internal Revenue Code. One key requirement is that the corporation must be a domestic entity. Additionally, the Internal Revenue Service (IRS) requires that an S corporation must not have more than 100 shareholders, all of whom should be individuals, certain trusts, or estates, and none can be non-resident aliens. It's important to file Form 2553 with the IRS on time to elect S corporation status. However, the late filing may still result in S corporation status if reasonable cause is shown. Moreover, an S corporation is permitted to have a fiscal tax year in certain circumstances, such as when a business can establish a natural business year or it falls under an exception in IRS regulations, making option d less likely to prevent the election compared to option c.