Final answer:
Magazines are the mass media form with disadvantages like long lead times for ad purchases, high costs, and uncertainty regarding ad positioning, making them less favorable compared to online and social media advertising.
Step-by-step explanation:
The mass media form that has the disadvantages of long ad-purchase lead time, high cost, and no guarantee of position is magazines. Unlike newspapers, which have adapted to social media, and radio, which is more effective in local elections, magazines require advertisers to plan and purchase ad space well in advance. Additionally, there is often a high cost associated with magazine advertising and no promise that the ad will be placed in a preferred or specific position within the publication. This contrasts with the more dynamic and cost-effective advertising opportunities provided by the Internet and social media campaigns, which have led to a diminishing role for print media in advertising strategies.