Which of the following activities must a registered representative report to his broker-dealer as an outside business activity (OBA)?

While volunteering demonstrates civic responsibility, it does not involve any financial compensation or business activity. Consequently, this type of volunteer work does not need to be reported as it does not create a potential conflict of interest or a business relationship that would require disclosure to a broker-dealer.

Owning a vacation home is a personal investment and does not constitute a business activity that generates income or requires registration. Such personal property ownership is not reportable as an outside business activity since it does not involve engaging in business or providing services.

This activity pertains to personal investment and does not fall under the category of outside business activities. Registered representatives can buy securities for their own accounts without needing to report them to their broker-dealer, as these transactions do not involve business dealings outside of their registered activities.