The most secure password reset process among the given options is to ask users to answer custom questions and then send a reset code via text. This method combines something the user knows (the answer to a custom question) with something the user has (access to a personal device that can receive a text), which aligns with the security principle of two-factor authentication, increasing the security of the reset process.
Reference: This method is frequently recommended in security best practices, including those covered by CompTIA IT Fundamentals, which emphasizes the importance of multi-factor authentication to enhance security.