Final answer:
Radio advertising is the least effective category of commercials due to the rise of social media and the internet. However, it may still be effective in local elections.
Step-by-step explanation:
The least effective category of commercials is radio advertising. While radio can reach a specific age group, it has been overshadowed by social media and the internet in terms of effectiveness and cost-efficiency. However, radio may still be impactful in local elections where it has a more localized reach.